Add FakeVideoDecoder.

media/filters/fake_demuxer_stream.cc

Index: media/filters/fake_demuxer_stream.cc
diff --git a/media/filters/fake_demuxer_stream.cc b/media/filters/fake_demuxer_stream.cc
index 3cc7fa666659735715142351482b1868583eb52d..ee2bc7ac60e2d51472bd29f1e237c8f9e4ada2a5 100644
--- a/media/filters/fake_demuxer_stream.cc
+++ b/media/filters/fake_demuxer_stream.cc
@@ -34,6 +34,7 @@ FakeDemuxerStream::FakeDemuxerStream(int num_configs,
       num_buffers_in_one_config_(num_buffers_in_one_config),
       is_encrypted_(is_encrypted),
       num_buffers_left_in_current_config_(num_buffers_in_one_config),
+      num_buffers_returned_(0),
       current_timestamp_(base::TimeDelta::FromMilliseconds(kStartTimestampMs)),
       duration_(base::TimeDelta::FromMilliseconds(kDurationMs)),
       next_coded_size_(kStartWidth, kStartHeight),
@@ -144,6 +145,7 @@ void FakeDemuxerStream::DoRead() {
     num_configs_left_--;
 
   base::ResetAndReturn(&read_cb_).Run(kOk, buffer);
+  num_buffers_returned_++;
 }
 
 }  // namespace media