tracing v2: Introduce TraceBufferWriter

components/tracing.gyp

Index: components/tracing.gyp
diff --git a/components/tracing.gyp b/components/tracing.gyp
index 7517d9cdc5a62976a8b2a9a1a2c6e564be79276f..1ea16ddd4e5051d2b07a6e8b598ddc2f34f519c9 100644
--- a/components/tracing.gyp
+++ b/components/tracing.gyp
@@ -49,6 +49,8 @@
         'tracing/core/proto_zero_message_handle.h',
         'tracing/core/scattered_stream_writer.cc',
         'tracing/core/scattered_stream_writer.h',
+        'tracing/core/trace_buffer_writer.cc',
+        'tracing/core/trace_buffer_writer.h',
         'tracing/core/trace_ring_buffer.cc',
         'tracing/core/trace_ring_buffer.h',
         'tracing/tracing_export.h',
@@ -97,5 +99,20 @@
       ],
       'includes': ['../build/protoc.gypi'],
     },
+    {
+      # Official protobuf used by tests to verify that the Tracing V2 output is
+      # effectively proto-compatible.
+      # GN version: //components/tracing:golden_protos_for_tests
+      'target_name': 'golden_protos_for_tests',
+      'type': 'static_library',
+      'variables': {
+        'proto_in_dir': 'tracing/proto',
+        'proto_out_dir': 'components/tracing/test/golden_protos',
+      },
+      'sources': [
+        'tracing/proto/events_chunk.proto',
+      ],
+      'includes': ['../build/protoc.gypi'],
+    },
   ],
 }