tracing v2: Introduce handles for safe usage of ProtoZeroMessage

components/tracing/core/proto_zero_message.cc

 // Copyright 2016 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.
 
 #include "components/tracing/core/proto_zero_message.h"
 
 #include <string.h>
 
 #include "components/tracing/core/proto_utils.h"
+#include "components/tracing/core/proto_zero_message_handle.h"
 
 #if !defined(ARCH_CPU_LITTLE_ENDIAN)
 // The memcpy() for float and double below needs to be adjusted if we want to
 // support big endian CPUs. There doesn't seem to be a compelling need today.
 #error big-endian CPUs not supported by this translation unit.
 #endif
 
 namespace tracing {
 namespace v2 {
 
@@ skipping 17 matching lines @@
 // This method is called to initialize both root and nested messages.
 void ProtoZeroMessage::Reset(ScatteredStreamWriter* stream_writer) {
   stream_writer_ = stream_writer;
   size_ = 0;
   size_field_.reset();
   size_already_written_ = 0;
   nested_message_ = nullptr;
   nesting_depth_ = 0;
 #if DCHECK_IS_ON()
   sealed_ = false;
+  handle_ = nullptr;
 #endif
 }
 
 void ProtoZeroMessage::AppendVarIntU64(uint32_t field_id, uint64_t value) {
   if (nested_message_)
     EndNestedMessage();
 
   uint8_t data[proto::GetMaxVarIntEncodedSize<uint32_t>() +
                proto::GetMaxVarIntEncodedSize<uint64_t>()];
   uint8_t* data_end;
@@ skipping 64 matching lines @@
     DCHECK_LT(size_, proto::kMaxMessageLength);
     DCHECK_EQ(proto::kMessageLengthFieldSize, size_field_.size());
     proto::WriteRedundantVarIntU32<proto::kMessageLengthFieldSize>(
         static_cast<uint32_t>(size_ - size_already_written_),
         size_field_.begin);
     size_field_.reset();
   }
 
 #if DCHECK_IS_ON()
   sealed_ = true;
+  if (handle_)
+    handle_->reset_message();
 #endif
 
   return size_;
 }
 
 void ProtoZeroMessage::BeginNestedMessageInternal(uint32_t field_id,
                                                   ProtoZeroMessage* message) {
   if (nested_message_)
     EndNestedMessage();
 
@@ skipping 15 matching lines @@
   nested_message_ = message;
 }
 
 void ProtoZeroMessage::EndNestedMessage() {
   size_ += nested_message_->Finalize();
   nested_message_ = nullptr;
 }
 
 }  // namespace v2
 }  // namespace tracing