Use a plain string buffer in MemoryLogWriter

Drop dependency on MemoryStream and the complex Stream interface.

Bug: None
Change-Id: I2226324b10ddbf5606e27bfecb82efdd25929163
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/213145
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33583}

test/logging/memory_log_writer.cc

diff --git a/test/logging/memory_log_writer.cc b/test/logging/memory_log_writer.cc
index 2eb1cff..f57f031 100644
--- a/test/logging/memory_log_writer.cc
+++ b/test/logging/memory_log_writer.cc
@@ -21,25 +21,18 @@
   explicit MemoryLogWriter(std::map<std::string, std::string>* target,
                            std::string filename)
       : target_(target), filename_(filename) {}
-  ~MemoryLogWriter() final {
-    size_t size;
-    buffer_.GetSize(&size);
-    target_->insert({filename_, std::string(buffer_.GetBuffer(), size)});
-  }
+  ~MemoryLogWriter() final { target_->insert({filename_, std::move(buffer_)}); }
   bool IsActive() const override { return true; }
   bool Write(const std::string& value) override {
-    size_t written;
-    int error;
-    return buffer_.WriteAll(value.data(), value.size(), &written, &error) ==
-           rtc::SR_SUCCESS;
-    RTC_DCHECK_EQ(value.size(), written);
+    buffer_.append(value);
+    return true;
   }
   void Flush() override {}
 
  private:
   std::map<std::string, std::string>* const target_;
   const std::string filename_;
-  rtc::MemoryStream buffer_;
+  std::string buffer_;
 };
 
 class MemoryLogWriterFactory : public LogWriterFactoryInterface {

test/logging/memory_log_writer.h

diff --git a/test/logging/memory_log_writer.h b/test/logging/memory_log_writer.h
index daef297..e795b2f 100644
--- a/test/logging/memory_log_writer.h
+++ b/test/logging/memory_log_writer.h
@@ -15,7 +15,6 @@
 #include <string>
 #include <vector>
 
-#include "rtc_base/memory_stream.h"
 #include "test/logging/log_writer.h"
 
 namespace webrtc {