tracing v2: Introduce TraceBufferWriter

components/tracing/test/fake_scattered_buffer.h

Index: components/tracing/test/fake_scattered_buffer.h
diff --git a/components/tracing/test/fake_scattered_buffer.h b/components/tracing/test/fake_scattered_buffer.h
index 5089765d2f208b035d9f6ddafbeb064501bc261c..f5d493788853ba54c870ef22fde4cd74aad0c65d 100644
--- a/components/tracing/test/fake_scattered_buffer.h
+++ b/components/tracing/test/fake_scattered_buffer.h
@@ -21,7 +21,7 @@ namespace v2 {
 class FakeScatteredBuffer : public ScatteredStreamWriter::Delegate {
  public:
   explicit FakeScatteredBuffer(size_t chunk_size);
-  ~FakeScatteredBuffer();
+  ~FakeScatteredBuffer() override;
 
   // ScatteredStreamWriter::Delegate implementation.
   ContiguousMemoryRange GetNewBuffer() override;