diff --git a/audio/test/low_bandwidth_audio_test.py b/audio/test/low_bandwidth_audio_test.py
index 6a95903..51273f7 100755
--- a/audio/test/low_bandwidth_audio_test.py
+++ b/audio/test/low_bandwidth_audio_test.py
@@ -286,7 +286,6 @@
         _LogCommand(test_command + [
             '--sample_rate_hz=%d' % analyzer.sample_rate_hz,
             '--test_case_prefix=%s' % analyzer.name,
-            '--write_histogram_proto_json'
           ] + args.extra_test_args),
         stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
     perf_results_file = None
diff --git a/test/BUILD.gn b/test/BUILD.gn
index d84a78b..29d5d6d 100644
--- a/test/BUILD.gn
+++ b/test/BUILD.gn
@@ -226,8 +226,6 @@
     "testsupport/perf_result_reporter.h",
     "testsupport/perf_test.cc",
     "testsupport/perf_test.h",
-    "testsupport/perf_test_graphjson_writer.cc",
-    "testsupport/perf_test_graphjson_writer.h",
     "testsupport/perf_test_histogram_writer.h",
     "testsupport/perf_test_result_writer.h",
   ]
diff --git a/test/test_main_lib.cc b/test/test_main_lib.cc
index f954a5e..15318b4 100644
--- a/test/test_main_lib.cc
+++ b/test/test_main_lib.cc
@@ -175,10 +175,10 @@
 #else
     int exit_code = RUN_ALL_TESTS();
 
-    std::string chartjson_result_file =
+    std::string perf_output_file =
         absl::GetFlag(FLAGS_isolated_script_test_perf_output);
-    if (!chartjson_result_file.empty()) {
-      if (!webrtc::test::WritePerfResults(chartjson_result_file)) {
+    if (!perf_output_file.empty()) {
+      if (!webrtc::test::WritePerfResults(perf_output_file)) {
         return 1;
       }
     }
diff --git a/test/testsupport/perf_test.cc b/test/testsupport/perf_test.cc
index 5b2f7a0..310c7e3 100644
--- a/test/testsupport/perf_test.cc
+++ b/test/testsupport/perf_test.cc
@@ -19,22 +19,26 @@
 
 #include "rtc_base/checks.h"
 #include "rtc_base/critical_section.h"
-#include "test/testsupport/perf_test_graphjson_writer.h"
 #include "test/testsupport/perf_test_histogram_writer.h"
 
-ABSL_FLAG(bool,
-          write_histogram_proto_json,
-          true,
-          "Use the histogram C++ API, which will write Histogram protos "
-          "instead of Chart JSON. See histogram.proto in third_party/catapult. "
-          "This flag only has effect  if --isolated_script_test_perf_output is "
-          "specified");
-
 namespace webrtc {
 namespace test {
 
 namespace {
 
+std::string UnitWithDirection(
+    const std::string& units,
+    webrtc::test::ImproveDirection improve_direction) {
+  switch (improve_direction) {
+    case webrtc::test::ImproveDirection::kNone:
+      return units;
+    case webrtc::test::ImproveDirection::kSmallerIsBetter:
+      return units + "_smallerIsBetter";
+    case webrtc::test::ImproveDirection::kBiggerIsBetter:
+      return units + "_biggerIsBetter";
+  }
+}
+
 template <typename Container>
 void OutputListToStream(std::ostream* ostream, const Container& values) {
   const char* sep = "";
@@ -192,13 +196,8 @@
 }
 
 PerfTestResultWriter& GetPerfWriter() {
-  if (absl::GetFlag(FLAGS_write_histogram_proto_json)) {
-    static PerfTestResultWriter* writer = CreateHistogramWriter();
-    return *writer;
-  } else {
-    static PerfTestResultWriter* writer = CreateGraphJsonWriter();
-    return *writer;
-  }
+  static PerfTestResultWriter* writer = CreateHistogramWriter();
+  return *writer;
 }
 
 }  // namespace
@@ -222,12 +221,7 @@
 
 bool WritePerfResults(const std::string& output_path) {
   std::string results = GetPerfResults();
-  FILE* output;
-  if (absl::GetFlag(FLAGS_write_histogram_proto_json)) {
-    output = fopen(output_path.c_str(), "wb");
-  } else {
-    output = fopen(output_path.c_str(), "w");
-  }
+  FILE* output = fopen(output_path.c_str(), "wb");
   if (output == NULL) {
     printf("Failed to write to %s.\n", output_path.c_str());
     return false;
diff --git a/test/testsupport/perf_test.h b/test/testsupport/perf_test.h
index 338a144..b0a5607 100644
--- a/test/testsupport/perf_test.h
+++ b/test/testsupport/perf_test.h
@@ -91,12 +91,11 @@
                  const bool important,
                  ImproveDirection improve_direction = ImproveDirection::kNone);
 
-// If --write_histogram_proto_json=false, this returns all perf results to date
-// in a JSON string formatted as described in dashboard/docs/data-format.md
-// in https://github.com/catapult-project/catapult/blob/master/. If
-// --write_histogram_proto_json=true, returns a string-encoded proto as
-// described in tracing/tracing/proto/histogram.proto in
+// Returns a string-encoded proto as described in
+// tracing/tracing/proto/histogram.proto in
 // https://github.com/catapult-project/catapult/blob/master/.
+// If you want to print the proto in human readable format, use
+// tracing/bin/proto2json from third_party/catapult in your WebRTC checkout.
 std::string GetPerfResults();
 
 // Print into stdout plottable metrics for further post processing.
@@ -122,7 +121,4 @@
 }  // namespace test
 }  // namespace webrtc
 
-// Only for use by tests.
-ABSL_DECLARE_FLAG(bool, write_histogram_proto_json);
-
 #endif  // TEST_TESTSUPPORT_PERF_TEST_H_
diff --git a/test/testsupport/perf_test_graphjson_writer.cc b/test/testsupport/perf_test_graphjson_writer.cc
deleted file mode 100644
index cf49b29..0000000
--- a/test/testsupport/perf_test_graphjson_writer.cc
+++ /dev/null
@@ -1,144 +0,0 @@
-/*
- *  Copyright (c) 2020 The WebRTC project authors. All Rights Reserved.
- *
- *  Use of this source code is governed by a BSD-style license
- *  that can be found in the LICENSE file in the root of the source
- *  tree. An additional intellectual property rights grant can be found
- *  in the file PATENTS.  All contributing project authors may
- *  be found in the AUTHORS file in the root of the source tree.
- */
-
-#include "test/testsupport/perf_test_graphjson_writer.h"
-
-#include <fstream>
-#include <map>
-#include <sstream>
-#include <string>
-#include <vector>
-
-#include "rtc_base/checks.h"
-#include "rtc_base/critical_section.h"
-
-namespace webrtc {
-namespace test {
-
-std::string UnitWithDirection(
-    const std::string& units,
-    webrtc::test::ImproveDirection improve_direction) {
-  switch (improve_direction) {
-    case webrtc::test::ImproveDirection::kNone:
-      return units;
-    case webrtc::test::ImproveDirection::kSmallerIsBetter:
-      return units + "_smallerIsBetter";
-    case webrtc::test::ImproveDirection::kBiggerIsBetter:
-      return units + "_biggerIsBetter";
-  }
-}
-
-template <typename Container>
-void OutputListToStream(std::ostream* ostream, const Container& values) {
-  const char* sep = "";
-  for (const auto& v : values) {
-    (*ostream) << sep << v;
-    sep = ",";
-  }
-}
-
-namespace {
-
-class PerfTestGraphJsonWriter : public PerfTestResultWriter {
- public:
-  PerfTestGraphJsonWriter() : crit_(), graphs_() {}
-  void ClearResults() {
-    rtc::CritScope lock(&crit_);
-    graphs_.clear();
-  }
-
-  void LogResult(const std::string& graph_name,
-                 const std::string& trace_name,
-                 const double value,
-                 const std::string& units,
-                 const bool important,
-                 webrtc::test::ImproveDirection improve_direction) {
-    std::ostringstream json_stream;
-    json_stream << '"' << trace_name << R"(":{)";
-    json_stream << R"("type":"scalar",)";
-    json_stream << R"("value":)" << value << ',';
-    json_stream << R"("units":")" << UnitWithDirection(units, improve_direction)
-                << R"("})";
-    rtc::CritScope lock(&crit_);
-    graphs_[graph_name].push_back(json_stream.str());
-  }
-
-  void LogResultMeanAndError(const std::string& graph_name,
-                             const std::string& trace_name,
-                             const double mean,
-                             const double error,
-                             const std::string& units,
-                             const bool important,
-                             webrtc::test::ImproveDirection improve_direction) {
-    std::ostringstream json_stream;
-    json_stream << '"' << trace_name << R"(":{)";
-    json_stream << R"("type":"list_of_scalar_values",)";
-    json_stream << R"("values":[)" << mean << "],";
-    json_stream << R"("std":)" << error << ',';
-    json_stream << R"("units":")" << UnitWithDirection(units, improve_direction)
-                << R"("})";
-    rtc::CritScope lock(&crit_);
-    graphs_[graph_name].push_back(json_stream.str());
-  }
-
-  void LogResultList(const std::string& graph_name,
-                     const std::string& trace_name,
-                     const rtc::ArrayView<const double> values,
-                     const std::string& units,
-                     const bool important,
-                     webrtc::test::ImproveDirection improve_direction) {
-    std::ostringstream value_stream;
-    value_stream.precision(8);
-    value_stream << '[';
-    OutputListToStream(&value_stream, values);
-    value_stream << ']';
-
-    std::ostringstream json_stream;
-    json_stream << '"' << trace_name << R"(":{)";
-    json_stream << R"("type":"list_of_scalar_values",)";
-    json_stream << R"("values":)" << value_stream.str() << ',';
-    json_stream << R"("units":")" << UnitWithDirection(units, improve_direction)
-                << R"("})";
-    rtc::CritScope lock(&crit_);
-    graphs_[graph_name].push_back(json_stream.str());
-  }
-
-  std::string Serialize() const {
-    std::ostringstream json_stream;
-    json_stream << R"({"format_version":"1.0",)";
-    json_stream << R"("charts":{)";
-    rtc::CritScope lock(&crit_);
-    for (auto graphs_it = graphs_.begin(); graphs_it != graphs_.end();
-         ++graphs_it) {
-      if (graphs_it != graphs_.begin())
-        json_stream << ',';
-      json_stream << '"' << graphs_it->first << "\":";
-      json_stream << '{';
-      OutputListToStream(&json_stream, graphs_it->second);
-      json_stream << '}';
-    }
-    json_stream << "}}";
-    return json_stream.str();
-  }
-
- private:
-  rtc::CriticalSection crit_;
-  std::map<std::string, std::vector<std::string>> graphs_
-      RTC_GUARDED_BY(&crit_);
-};
-
-}  // namespace
-
-PerfTestResultWriter* CreateGraphJsonWriter() {
-  return new PerfTestGraphJsonWriter();
-}
-
-}  // namespace test
-}  // namespace webrtc
diff --git a/test/testsupport/perf_test_graphjson_writer.h b/test/testsupport/perf_test_graphjson_writer.h
deleted file mode 100644
index ae32cfa..0000000
--- a/test/testsupport/perf_test_graphjson_writer.h
+++ /dev/null
@@ -1,32 +0,0 @@
-/*
- *  Copyright (c) 2020 The WebRTC project authors. All Rights Reserved.
- *
- *  Use of this source code is governed by a BSD-style license
- *  that can be found in the LICENSE file in the root of the source
- *  tree. An additional intellectual property rights grant can be found
- *  in the file PATENTS.  All contributing project authors may
- *  be found in the AUTHORS file in the root of the source tree.
- */
-
-#ifndef TEST_TESTSUPPORT_PERF_TEST_GRAPHJSON_WRITER_H_
-#define TEST_TESTSUPPORT_PERF_TEST_GRAPHJSON_WRITER_H_
-
-#include <string>
-
-#include "test/testsupport/perf_test.h"
-#include "test/testsupport/perf_test_result_writer.h"
-
-namespace webrtc {
-namespace test {
-
-PerfTestResultWriter* CreateGraphJsonWriter();
-
-// Utilities that happen to be useful to perf_test.cc. Just move these back
-// to perf_test.cc when this file goes away.
-std::string UnitWithDirection(const std::string& units,
-                              webrtc::test::ImproveDirection improve_direction);
-
-}  // namespace test
-}  // namespace webrtc
-
-#endif  // TEST_TESTSUPPORT_PERF_TEST_GRAPHJSON_WRITER_H_
diff --git a/test/testsupport/perf_test_unittest.cc b/test/testsupport/perf_test_unittest.cc
index d99014b..b779f4c 100644
--- a/test/testsupport/perf_test_unittest.cc
+++ b/test/testsupport/perf_test_unittest.cc
@@ -22,47 +22,6 @@
 namespace proto = catapult::tracing::tracing::proto;
 #endif
 
-namespace {
-
-const char* kJsonExpected = R"({
-  "format_version":"1.0",
-  "charts":{
-    "foobar":{
-      "baz_v":{
-        "type":"scalar",
-        "value":7,
-        "units":"widgets"
-      },
-      "baz_me":{
-        "type":"list_of_scalar_values",
-        "values":[1],
-        "std":2,
-        "units":"lemurs"
-      },
-      "baz_vl":{
-        "type":"list_of_scalar_values",
-        "values":[1,2,3],
-        "units":"units"
-      }
-    },
-    "measurementmodifier":{
-      "trace":{
-        "type":"scalar",
-        "value":42,
-        "units":"units"
-      }
-    }
-  }
-})";
-
-std::string RemoveSpaces(std::string s) {
-  s.erase(std::remove(s.begin(), s.end(), ' '), s.end());
-  s.erase(std::remove(s.begin(), s.end(), '\n'), s.end());
-  return s;
-}
-
-}  // namespace
-
 namespace webrtc {
 namespace test {
 
@@ -96,21 +55,6 @@
   EXPECT_EQ(expected, ::testing::internal::GetCapturedStdout());
 }
 
-TEST_F(PerfTest, TestGetPerfResultsJSON) {
-  bool original_flag = absl::GetFlag(FLAGS_write_histogram_proto_json);
-  absl::SetFlag(&FLAGS_write_histogram_proto_json, false);
-
-  PrintResult("measurement", "modifier", "trace", 42, "units", false);
-  PrintResult("foo", "bar", "baz_v", 7, "widgets", true);
-  PrintResultMeanAndError("foo", "bar", "baz_me", 1, 2, "lemurs", false);
-  const double kListOfScalars[] = {1, 2, 3};
-  PrintResultList("foo", "bar", "baz_vl", kListOfScalars, "units", false);
-
-  EXPECT_EQ(RemoveSpaces(kJsonExpected), GetPerfResults());
-
-  absl::SetFlag(&FLAGS_write_histogram_proto_json, original_flag);
-}
-
 TEST_F(PerfTest, TestClearPerfResults) {
   PrintResult("measurement", "modifier", "trace", 42, "units", false);
   ClearPerfResults();
@@ -158,16 +102,6 @@
   EXPECT_EQ(hist2.unit().unit(), proto::MS_BEST_FIT_FORMAT);
 }
 
-TEST_F(PerfTest, TestClearPerfResultsHistograms) {
-  bool original_flag = absl::GetFlag(FLAGS_write_histogram_proto_json);
-  absl::SetFlag(&FLAGS_write_histogram_proto_json, true);
-  PrintResult("measurement", "modifier", "trace", 42, "ms", false);
-  ClearPerfResults();
-  EXPECT_EQ("", GetPerfResults());
-
-  absl::SetFlag(&FLAGS_write_histogram_proto_json, original_flag);
-}
-
 #endif  // WEBRTC_ENABLE_PROTOBUF
 
 #if GTEST_HAS_DEATH_TEST