tracing v2: Introduce handles for safe usage of ProtoZeroMessage

components/tracing/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//third_party/protobuf/proto_library.gni")
 
 component("tracing") {
   sources = [
     "child/child_memory_dump_manager_delegate_impl.cc",
     "child/child_memory_dump_manager_delegate_impl.h",
     "child/child_trace_message_filter.cc",
     "child/child_trace_message_filter.h",
     "common/graphics_memory_dump_provider_android.cc",
     "common/graphics_memory_dump_provider_android.h",
     "common/process_metrics_memory_dump_provider.cc",
     "common/process_metrics_memory_dump_provider.h",
     "common/tracing_messages.cc",
     "common/tracing_messages.h",
     "core/proto_utils.h",
     "core/proto_zero_message.cc",
     "core/proto_zero_message.h",
+    "core/proto_zero_message_handle.cc",
+    "core/proto_zero_message_handle.h",
     "core/scattered_stream_writer.cc",
     "core/scattered_stream_writer.h",
     "core/trace_ring_buffer.cc",
     "core/trace_ring_buffer.h",
     "tracing_export.h",
   ]
 
   defines = [ "TRACING_IMPLEMENTATION" ]
 
   deps = [
@@ skipping 78 matching lines @@
     "//ipc",
     "//testing/gmock:gmock",
     "//testing/gtest",
   ]
 
   if (!is_android) {
     sources += [ "browser/trace_config_file_unittest.cc" ]
     deps += [ ":startup_tracing" ]
   }
 }