Revert to zero-initializing buffers for FFmpegVideoDecoder

media/filters/ffmpeg_video_decoder.cc

Index: media/filters/ffmpeg_video_decoder.cc
diff --git a/media/filters/ffmpeg_video_decoder.cc b/media/filters/ffmpeg_video_decoder.cc
index c196590478723611b19ca3c2e3c236352dbd0016..ccc07572848ebf4a2bb0fe1cd8dc2bb30018122b 100644
--- a/media/filters/ffmpeg_video_decoder.cc
+++ b/media/filters/ffmpeg_video_decoder.cc
@@ -115,12 +115,10 @@ int FFmpegVideoDecoder::GetVideoBuffer(struct AVCodecContext* codec_context,
     return AVERROR(EINVAL);
   }
 
+  // FFmpeg expects the initialize allocation to be zero-initialized.  Failure
+  // to do so can lead to unitialized value usage.  See http://crbug.com/390941
   scoped_refptr<VideoFrame> video_frame = frame_pool_.CreateFrame(
-      format, coded_size, gfx::Rect(size), natural_size, kNoTimestamp());
-#if defined(MEMORY_SANITIZER)
-  MSAN_UNPOISON(video_frame->data(0),
-                VideoFrame::AllocationSize(format, coded_size));
-#endif
+      format, coded_size, gfx::Rect(size), natural_size, kNoTimestamp(), true);

[miu, 2015/08/04 20:16:22]

Instead of adding this extra bool parameter to VideoFramePool::CreateFrame(),
you should just memset the memory here in ffmpeg_video_decoder.cc.  This seems
to be the only place where the memory is required to be initialized.

[miu, 2015/08/06 21:23:30]

OIC.  Hmm...now I'm thinking we ought to just always zero-out the VideoFrames
the first time they're created in the pool.  This is only a one-time cost, so it
shouldn't be a huge performance problem for the non-FFMPEG modules that do not
need the zero-initialization.  WDYT?

[DaleCurtis, 2015/08/07 00:56:02]

That's fine with me, in a pool the one-time cost should be low.

 
   // Prefer the color space from the codec context. If it's not specified (or is
   // set to an unsupported value), fall back on the value from the config.
@@ -131,7 +129,7 @@ int FFmpegVideoDecoder::GetVideoBuffer(struct AVCodecContext* codec_context,
   video_frame->metadata()->SetInteger(VideoFrameMetadata::COLOR_SPACE,
                                       color_space);
 
-  for (int i = 0; i < 3; i++) {
+  for (size_t i = 0; i < VideoFrame::NumPlanes(video_frame->format()); i++) {
     frame->data[i] = video_frame->data(i);
     frame->linesize[i] = video_frame->stride(i);
   }