AU: Speed up updates by using buffered writes.

file_writer_mock.h

Index: file_writer_mock.h
diff --git a/file_writer_mock.h b/file_writer_mock.h
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+// Copyright (c) 2010 The Chromium OS 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 CHROMEOS_PLATFORM_UPDATE_ENGINE_FILE_WRITER_MOCK_H__
+#define CHROMEOS_PLATFORM_UPDATE_ENGINE_FILE_WRITER_MOCK_H__
+
+#include "gmock/gmock.h"
+#include "update_engine/file_writer.h"
+
+namespace chromeos_update_engine {
+
+class FileWriterMock : public FileWriter {
+ public:
+  MOCK_METHOD3(Open, int(const char* path, int flags, mode_t mode));
+  MOCK_METHOD2(Write, ssize_t(const void* bytes, size_t count));
+  MOCK_METHOD0(Close, int());
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_FILE_WRITER_MOCK_H__