Use mime type for image extension

components/image_fetcher/request_metadata.h

+// Copyright 2017 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_IMAGE_FETCHER_REQUEST_METADATA_H_
+#define COMPONENTS_IMAGE_FETCHER_REQUEST_METADATA_H_
+
+#include <string>
+
+namespace image_fetcher {
+
+struct RequestMetadata {
+  std::string mime_type;
+};
+
+bool operator==(const RequestMetadata& lhs, const RequestMetadata& rhs);
+bool operator!=(const RequestMetadata& lhs, const RequestMetadata& rhs);
+
+}  // namespace image_fetcher
+
+#endif  // COMPONENTS_IMAGE_FETCHER_REQUEST_METADATA_H_