tracing v2: refactor fake_scattered_buffer class for tests

components/tracing/test/fake_scattered_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_TEST_FAKE_SCATTERED_BUFFER_H_
+#define COMPONENTS_TRACING_TEST_FAKE_SCATTERED_BUFFER_H_
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "base/macros.h"
+#include "components/tracing/core/scattered_stream_writer.h"
+#include "components/tracing/tracing_export.h"
+
+namespace tracing {
+namespace v2 {
+
+// A simple ScatteredStreamWriter::Delegate implementation which just allocates
+// chunks of a fixed size.
+class FakeScatteredBuffer : public ScatteredStreamWriter::Delegate {
+ public:
+  explicit FakeScatteredBuffer(size_t chunk_size);
+  ~FakeScatteredBuffer();
+
+  // ScatteredStreamWriter::Delegate implementation.
+  ContiguousMemoryRange GetNewBuffer() override;
+
+  std::string GetChunkAsString(int chunk_index);
+
+  std::string GetBytesAsString(size_t start, size_t length);
+
+  const std::vector<std::unique_ptr<uint8_t[]>>& chunks() const {
+    return chunks_;
+  }
+
+ private:
+  const size_t chunk_size_;
+  std::vector<std::unique_ptr<uint8_t[]>> chunks_;
+
+  DISALLOW_COPY_AND_ASSIGN(FakeScatteredBuffer);
+};
+
+}  // namespace v2
+}  // namespace tracing
+
+#endif  // COMPONENTS_TRACING_TEST_FAKE_SCATTERED_BUFFER_H_