Fix VideoDecoderShim to return correct decode_id for all codecs.

media/base/video_decoder.h

Index: media/base/video_decoder.h
diff --git a/media/base/video_decoder.h b/media/base/video_decoder.h
index d7e7a791de3d168668476cbdbd73aae22dd90ef4..505248222119b6bee0776ae428674093280b8e4b 100644
--- a/media/base/video_decoder.h
+++ b/media/base/video_decoder.h
@@ -78,8 +78,9 @@ class MEDIA_EXPORT VideoDecoder {
   // called again).
   //
   // After decoding is finished the decoder calls |output_cb| specified in
-  // Initialize() for each decoded frame. |output_cb| may be called before or
-  // after |decode_cb|.
+  // Initialize() for each decoded frame. In general |output_cb| may be called
+  // before or after |decode_cb|, but software decoders must call |output_cb|

[xhwang, 2015/01/22 23:52:43]

I get what you mean, but this can be complicated. For example, the hardware
decoder (GpuVideoDecoder) on Mac can fallback to software mode internally. 

I suggest you do the same as |low_delay| where VideoDecoderShim assumes FFVD and
VPxVD always do this and relax this requirement to a recommendation. But it's up
to you :)

[Sergey Ulanov, 2015/01/23 00:19:37]

Done.

+  // before calling |decode_cb|, i.e. while Decode() is pending.
   //
   // If |buffer| is an EOS buffer then the decoder must be flushed, i.e.
   // |output_cb| must be called for each frame pending in the queue and