Spec compliant video constraints for getUserMedia behind flag.

content/renderer/media/mock_media_stream_video_source.h

Index: content/renderer/media/mock_media_stream_video_source.h
diff --git a/content/renderer/media/mock_media_stream_video_source.h b/content/renderer/media/mock_media_stream_video_source.h
index 4a44e03f478a40a260a7328302dfdb0f2443d46a..7c4746e23ab3a285cac4bba78596219560342649 100644
--- a/content/renderer/media/mock_media_stream_video_source.h
+++ b/content/renderer/media/mock_media_stream_video_source.h
@@ -17,6 +17,8 @@ class MockMediaStreamVideoSource : public MediaStreamVideoSource {
   explicit MockMediaStreamVideoSource(bool manual_get_supported_formats);
   MockMediaStreamVideoSource(bool manual_get_supported_formats,
                              bool respond_to_request_refresh_frame);
+  MockMediaStreamVideoSource(const media::VideoCaptureFormat& format,
+                             bool respond_to_request_refresh_frame);
   virtual ~MockMediaStreamVideoSource();
 
   MOCK_METHOD1(DoSetMutedState, void(bool muted_state));
@@ -67,6 +69,8 @@ class MockMediaStreamVideoSource : public MediaStreamVideoSource {
       const blink::WebMediaConstraints& constraints,
       const VideoCaptureDeliverFrameCB& frame_callback) override;
   void StopSourceImpl() override;
+  base::Optional<media::VideoCaptureFormat> GetCurrentFormatImpl()
+      const override;
 
  private:
   media::VideoCaptureFormat format_;