Detect HAVE_NOTHING during pending Demuxer read as network underflow

Adds BufferingStateChangeReason to the OnBufferingStateChange() methods
for both RendererClient and Pipeline::Client interfaces. See
buffering_state.h for reason values and meanings.

Bug: 912795
Change-Id: I53be9c19fabb71e60b2ae8d563722f20ed7d3455
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1682893
Commit-Queue: Chrome Cunningham <chcunningham@chromium.org>
Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Auto-Submit: Chrome Cunningham <chcunningham@chromium.org>
Cr-Commit-Position: refs/heads/master@{#679685}

diff --git a/media/renderers/renderer_impl.h b/media/renderers/renderer_impl.h
index dc510254ef..379be97 100644
--- a/media/renderers/renderer_impl.h
+++ b/media/renderers/renderer_impl.h

@@ -166,7 +166,8 @@
   //   - A non-waiting to waiting transition indicates underflow has occurred
   //     and PausePlayback() should be called
   void OnBufferingStateChange(DemuxerStream::Type type,
-                              BufferingState new_buffering_state);
+                              BufferingState new_buffering_state,
+                              BufferingStateChangeReason reason);
 
   // Handles the buffering notifications that we might get while an audio or a
   // video stream is being restarted. In those cases we don't want to report