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

components/tracing/core/trace_ring_buffer_unittest.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/trace_ring_buffer.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace tracing {
 namespace v2 {
 
 namespace {
 
-const size_t kChunkSize = TraceRingBuffer::Chunk::kSize;
-
 TEST(TraceRingBufferTest, BasicChunkWrapping) {
   const uint32_t kNumChunks = 5;
   const size_t kBufferSize = kChunkSize * kNumChunks;
   std::unique_ptr<uint8_t[]> storage(new uint8_t[kBufferSize]);
   TraceRingBuffer ring_buffer(storage.get(), kBufferSize);
 
   EXPECT_EQ(0u, ring_buffer.GetNumChunksTaken());
   uint8_t* last_chunk_end = nullptr;
 
   // Fill the buffer twice to test wrapping logic.
@@ skipping 17 matching lines @@
     uint8_t* chunk_start = storage.get() + (chunk_idx * kChunkSize);
     const uint32_t kPayloadSize = (chunk_idx + 1) * 8;
     EXPECT_EQ(kPayloadSize, *reinterpret_cast<uint32_t*>(chunk_start));
     for (uint32_t i = 0; i < kPayloadSize; ++i)
       EXPECT_EQ(chunk_idx + 1, *(chunk_start + sizeof(uint32_t) + i));
   }
 }
 
 TEST(TraceRingBufferTest, ChunkBankrupcyDoesNotCrash) {
   const size_t kNumChunks = 2;
-  const size_t kBufferSize = TraceRingBuffer::Chunk::kSize * kNumChunks;
+  const size_t kBufferSize = kChunkSize * kNumChunks;
   std::unique_ptr<uint8_t[]> storage(new uint8_t[kBufferSize]);
   TraceRingBuffer ring_buffer(storage.get(), kBufferSize);
 
   TraceRingBuffer::Chunk* chunk1 = ring_buffer.TakeChunk(1);
   ASSERT_NE(nullptr, chunk1);
 
   TraceRingBuffer::Chunk* chunk2 = ring_buffer.TakeChunk(1);
   ASSERT_NE(nullptr, chunk2);
 
   EXPECT_EQ(2u, ring_buffer.GetNumChunksTaken());
@@ skipping 13 matching lines @@
   ring_buffer.ReturnChunk(chunk2);
   EXPECT_EQ(1u, ring_buffer.GetNumChunksTaken());
   TraceRingBuffer::Chunk* chunk = ring_buffer.TakeChunk(1);
   ASSERT_NE(nullptr, chunk);
   ASSERT_FALSE(ring_buffer.IsBankrupcyChunkForTesting(chunk));
 }
 
 }  // namespace
 }  // namespace v2
 }  // namespace tracing