Add EncodedImageCallback::OnEncodedImage().

OnEncodedImage() is going to replace Encoded(), which is deprecated now.
The new OnEncodedImage() returns Result struct that contains frame_id,
which tells the encoder RTP timestamp for the frame.

BUG=chromium:621691
R=niklas.enbom@webrtc.org, sprang@webrtc.org, stefan@webrtc.org

Review URL: https://codereview.webrtc.org/2089773002 .

Committed: https://crrev.com/ad34dbe934d47f88011045671b4aea00dbd5a795
Cr-Original-Commit-Position: refs/heads/master@{#13613}
Cr-Commit-Position: refs/heads/master@{#13615}

webrtc/modules/video_coding/include/mock/mock_video_codec_interface.h

@@ -22,10 +22,10 @@ namespace webrtc {
 
 class MockEncodedImageCallback : public EncodedImageCallback {
  public:
-  MOCK_METHOD3(Encoded,
-               int32_t(const EncodedImage& encodedImage,
-                       const CodecSpecificInfo* codecSpecificInfo,
-                       const RTPFragmentationHeader* fragmentation));
+  MOCK_METHOD3(OnEncodedImage,
+               Result(const EncodedImage& encodedImage,
+                      const CodecSpecificInfo* codecSpecificInfo,
+                      const RTPFragmentationHeader* fragmentation));
 };
 
 class MockVideoEncoder : public VideoEncoder {