Add usage message to reference_less_video_analysis.

Bug: webrtc:10616
Change-Id: Ibbaba9ec6a74466021e70d01f3a8ff4c3fd212b3
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/146205
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28611}
diff --git a/rtc_tools/BUILD.gn b/rtc_tools/BUILD.gn
index f774343..a982265 100644
--- a/rtc_tools/BUILD.gn
+++ b/rtc_tools/BUILD.gn
@@ -231,6 +231,7 @@
       ":reference_less_video_analysis_lib",
       "//third_party/abseil-cpp/absl/flags:flag",
       "//third_party/abseil-cpp/absl/flags:parse",
+      "//third_party/abseil-cpp/absl/flags:usage",
     ]
   }
 
diff --git a/rtc_tools/frame_analyzer/reference_less_video_analysis.cc b/rtc_tools/frame_analyzer/reference_less_video_analysis.cc
index 42ee18f..fca89a8 100644
--- a/rtc_tools/frame_analyzer/reference_less_video_analysis.cc
+++ b/rtc_tools/frame_analyzer/reference_less_video_analysis.cc
@@ -14,6 +14,7 @@
 
 #include "absl/flags/flag.h"
 #include "absl/flags/parse.h"
+#include "absl/flags/usage.h"
 #include "rtc_tools/frame_analyzer/reference_less_video_analysis_lib.h"
 
 ABSL_FLAG(std::string,
@@ -23,18 +24,13 @@
           "supported");
 
 int main(int argc, char* argv[]) {
+  absl::SetProgramUsageMessage(
+      "Outputs the freezing score by comparing "
+      "current frame with the previous frame.\n"
+      "Example usage:\n"
+      "./reference_less_video_analysis "
+      "--video_file=video_file.y4m\n");
   absl::ParseCommandLine(argc, argv);
-  // TODO(bugs.webrtc.org/10616): Add program usage message when Abseil
-  // flags supports it.
-  // This captures the freezing metrics for reference less video analysis.
-  // std::string usage =
-  //     "Outputs the freezing score by comparing current frame "
-  //     "with the previous frame.\nExample usage:\n" +
-  //     program_name +
-  //     " --video_file=video_file.y4m\n"
-  //     "Command line flags:\n"
-  //     "  - video_file(string): Path of the video "
-  //     "file to be analyzed. Only y4m file format is supported.\n";
 
   std::string video_file = absl::GetFlag(FLAGS_video_file);
   if (video_file.empty()) {