tracing v2: Add proto_utils.h

components/tracing/core/scattered_stream_writer.h

 // 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.
 
 #ifndef COMPONENTS_TRACING_CORE_SCATTERED_STREAM_WRITER_H_
 #define COMPONENTS_TRACING_CORE_SCATTERED_STREAM_WRITER_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "components/tracing/tracing_export.h"
 
 namespace tracing {
 namespace v2 {
 
 struct ContiguousMemoryRange {
   uint8_t* begin;
   uint8_t* end;  // STL style: one byte past the end of the buffer.
+
+  inline bool is_valid() const { return begin != nullptr; }
+  inline void reset() { begin = nullptr; }
+  inline size_t size() { return static_cast<size_t>(end - begin); }
 };
 
 // This class deals with the following problem: append-only proto messages want
 // to write a stream of bytes, without caring about the implementation of the
 // underlying buffer (which concretely will be either the trace ring buffer
 // or a heap-allocated buffer). The main deal is: proto messages don't know in
 // advance what their size will be.
 // Due to the tracing buffer being split into fixed-size chunks, on some
 // occasions, these writes need to be spread over two (or more) non-contiguous
 // chunks of memory. Similarly, when the buffer is backed by the heap, we want
@@ skipping 38 matching lines @@
   ContiguousMemoryRange cur_range_;
   uint8_t* write_ptr_;
 
   DISALLOW_COPY_AND_ASSIGN(ScatteredStreamWriter);
 };
 
 }  // namespace v2
 }  // namespace tracing
 
 #endif  // COMPONENTS_TRACING_CORE_SCATTERED_STREAM_WRITER_H_