Use mime type for image extension

components/image_fetcher/request_metadata.h

Index: components/image_fetcher/request_metadata.h
diff --git a/components/image_fetcher/request_metadata.h b/components/image_fetcher/request_metadata.h
new file mode 100644
index 0000000000000000000000000000000000000000..1bc997a765285ac6323630a562920d7eca5e2c32
--- /dev/null
+++ b/components/image_fetcher/request_metadata.h
@@ -0,0 +1,21 @@
+// 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_