Reland of tracing v2: Introduce TraceBufferWriter (https://codereview.chromium.org/2196663002)

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/logging.h"
@@ skipping 20 matching lines @@
 // 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
 // to avoid realloc() calls, as they might cause a full copy of the contents
 // of the buffer.
 // The purpose of this class is to abtract away the non-contiguous write logic.
 // This class knows how to deal with writes as long as they fall in the same
 // ContiguousMemoryRange and defers the chunk-chaining logic to the Delegate.
 class TRACING_EXPORT ScatteredStreamWriter {
  public:
-  class Delegate {
+  class TRACING_EXPORT Delegate {
    public:
+    virtual ~Delegate();
     virtual ContiguousMemoryRange GetNewBuffer() = 0;
   };
 
   explicit ScatteredStreamWriter(Delegate* delegate);
   ~ScatteredStreamWriter();
 
   void WriteByte(uint8_t value);
   void WriteBytes(const uint8_t* src, size_t size);
 
   // Reserves a fixed amount of bytes to be backfilled later. The reserved range
@@ skipping 29 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_