Plumb callbacks from mojo media service to client.

media/mojo/interfaces/media_types.mojom

Index: media/mojo/interfaces/media_types.mojom
diff --git a/media/mojo/interfaces/media_types.mojom b/media/mojo/interfaces/media_types.mojom
index bef1de32d219e51000c620392157074bb1c886e6..5f9a4f07de6cf65bca26251d1a90006a44a5c09b 100644
--- a/media/mojo/interfaces/media_types.mojom
+++ b/media/mojo/interfaces/media_types.mojom
@@ -336,3 +336,12 @@ struct VideoFrame {
   uint64 u_offset;
   uint64 v_offset;
 };
+
+struct PipelineStatistics {
+  uint64 audio_bytes_decoded;
+  uint64 video_bytes_decoded;
+  uint32 video_frames_decoded;
+  uint32 video_frames_dropped;
+  int64 audio_memory_usage;

[dcheng, 2016/07/07 04:19:37]

Is there a reason for this to be signed (other than the fact that the existing
one in C++ is signed)? Can memory usage be reported as negative for some reason?

[slan, 2016/07/07 16:41:45]

Original justification:
https://codereview.chromium.org/1409123005/diff/1/media/filters/chunk_demuxer.cc

This is now used to calculate a delta in WebMediaPlayer, which must be expressed
as int64_t, so it avoids a cast there:
https://cs.chromium.org/chromium/src/media/blink/webmediaplayer_impl.cc?rcl=0...

+  int64 video_memory_usage;
+};