MediaLog: Log selected audio/video decoder name.

media/base/mock_filters.cc

Index: media/base/mock_filters.cc
diff --git a/media/base/mock_filters.cc b/media/base/mock_filters.cc
index 4bb03e4dbde626560e197464acbd4ac686d44046..55d7eb56a80846cf1282a98152e750f2f515a5e8 100644
--- a/media/base/mock_filters.cc
+++ b/media/base/mock_filters.cc
@@ -52,10 +52,18 @@ VideoRotation MockDemuxerStream::video_rotation() {
   return VIDEO_ROTATION_0;
 }
 
+std::string MockVideoDecoder::GetDisplayName() const {
+  return "MockVideoDecoder";
+}
+
 MockVideoDecoder::MockVideoDecoder() {
   EXPECT_CALL(*this, HasAlpha()).WillRepeatedly(Return(false));
 }
 
+std::string MockAudioDecoder::GetDisplayName() const {
+  return "MockAudioDecoder";
+}
+
 MockVideoDecoder::~MockVideoDecoder() {}
 
 MockAudioDecoder::MockAudioDecoder() {}