Implement ChromeOS mime type extension mappings.

net/base/mime_extension_chromeos.h

+// Copyright 2015 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 NET_BASE_MIME_EXTENSION_CHROMEOS_H_
+#define NET_BASE_MIME_EXTENSION_CHROMEOS_H_
+
+#include <string>
+
+#include "base/files/file_path.h"
+
+namespace net {
+namespace chromeos {
+
+bool GetPlatformMimeTypeFromExtension(const base::FilePath::StringType& ext,
+                                      std::string* mime_type);
+
+}  // namespace chromeos
+}  // namespace net
+
+#endif  // NET_BASE_MIME_EXTENSION_CHROMEOS_H_