Use mime type for image extension

components/image_fetcher/image_data_fetcher.h

Index: components/image_fetcher/image_data_fetcher.h
diff --git a/components/image_fetcher/image_data_fetcher.h b/components/image_fetcher/image_data_fetcher.h
index 5383086a519b2aa37324ab4335a5df99ef229d1e..c4d72d1438c18ca622e7cf3374aeb557c6514ed3 100644
--- a/components/image_fetcher/image_data_fetcher.h
+++ b/components/image_fetcher/image_data_fetcher.h
@@ -27,7 +27,8 @@ namespace image_fetcher {
 class ImageDataFetcher : public net::URLFetcherDelegate {
  public:
   using ImageDataFetcherCallback =
-      base::Callback<void(const std::string& image_data)>;
+      base::Callback<void(const std::string& image_data,
+                          const std::string& mime_type)>;

[Marc Treib, 2017/02/09 12:34:45]

Your other pending CL adds a response_code parameter here; this is another one.
It's not good that all clients have to be updated every time we add a new piece
of metadata here. How about wrapping all the metadata in a struct? Then existing
clients don't have to care about any added fields.

[gambard, 2017/02/09 13:44:12]

Good idea!

 
   using DataUseServiceName = data_use_measurement::DataUseUserData::ServiceName;