Add methods for telling V8 how much memory audio/video is using.

media/filters/ffmpeg_demuxer_unittest.cc

Index: media/filters/ffmpeg_demuxer_unittest.cc
diff --git a/media/filters/ffmpeg_demuxer_unittest.cc b/media/filters/ffmpeg_demuxer_unittest.cc
index 2e988d2ccb37df1f6f4e1a85f0cbf2b1d68d2339..1e915b943d4f06d5ebeb156d7947c570c5afa9dc 100644
--- a/media/filters/ffmpeg_demuxer_unittest.cc
+++ b/media/filters/ffmpeg_demuxer_unittest.cc
@@ -399,6 +399,8 @@ TEST_F(FFmpegDemuxerTest, Read_Audio) {
 
   audio->Read(NewReadCB(FROM_HERE, 27, 3000, true));
   message_loop_.Run();
+
+  EXPECT_EQ(22084, demuxer_->GetMemoryUsage());
 }
 
 TEST_F(FFmpegDemuxerTest, Read_Video) {
@@ -414,6 +416,8 @@ TEST_F(FFmpegDemuxerTest, Read_Video) {
 
   video->Read(NewReadCB(FROM_HERE, 1057, 33000, false));
   message_loop_.Run();
+
+  EXPECT_EQ(323, demuxer_->GetMemoryUsage());
 }
 
 TEST_F(FFmpegDemuxerTest, Read_Text) {