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

components/tracing/core/trace_ring_buffer.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_TRACE_RING_BUFFER_H_
 #define COMPONENTS_TRACING_CORE_TRACE_RING_BUFFER_H_
 
 #include <memory>
 
 #include "base/atomicops.h"
 #include "base/macros.h"
 #include "base/synchronization/lock.h"
 #include "components/tracing/tracing_export.h"
 
 namespace tracing {
 namespace v2 {
 
 static const uint32_t kNoChunkOwner = 0;
+static const size_t kChunkSize = 32 * 1024;
 
 class TRACING_EXPORT TraceRingBuffer {
  public:
   class Chunk {
    public:
     using Header = base::subtle::Atomic32;
-    static constexpr size_t kSize = 32 * 1024;
 
     Chunk();
     ~Chunk();
 
     void Initialize(uint8_t* begin);
     void Clear();
 
     uint8_t* begin() const { return begin_; }
     Header* header() const { return reinterpret_cast<Header*>(begin_); }
     uint8_t* payload() const { return begin_ + sizeof(Header); }
-    uint8_t* end() const { return begin_ + kSize; }
+    uint8_t* end() const { return begin_ + kChunkSize; }
 
     void set_used_size(uint32_t size) {
       base::subtle::NoBarrier_Store(header(), size);
     }
     uint32_t used_size() const {
       return base::subtle::NoBarrier_Load(header());
     }
 
     void set_next_in_owner_list(Chunk* next) { next_in_owner_list_ = next; }
     Chunk* next_in_owner_list() const { return next_in_owner_list_; }
@@ skipping 48 matching lines @@
   Chunk bankrupcy_chunk_;
   std::unique_ptr<uint8_t[]> bankrupcy_chunk_storage_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceRingBuffer);
 };
 
 }  // namespace v2
 }  // namespace tracing
 
 #endif  // COMPONENTS_TRACING_CORE_TRACE_RING_BUFFER_H_