Refactor audio and video decoder status into common file.

media/cast/sender/h264_vt_encoder_unittest.cc

Index: media/cast/sender/h264_vt_encoder_unittest.cc
diff --git a/media/cast/sender/h264_vt_encoder_unittest.cc b/media/cast/sender/h264_vt_encoder_unittest.cc
index 45fd52d5dfd669c38461ce33909e7611dcdbf8a3..054ec41fee7651c9c35e2eb9813a1df8edf3420d 100644
--- a/media/cast/sender/h264_vt_encoder_unittest.cc
+++ b/media/cast/sender/h264_vt_encoder_unittest.cc
@@ -167,9 +167,7 @@ class EndToEndFrameChecker
     ++count_frames_checked_;
   }
 
-  void DecodeDone(VideoDecoder::Status status) {
-    EXPECT_EQ(VideoDecoder::kOk, status);
-  }
+  void DecodeDone(DecodeStatus status) { EXPECT_EQ(DecodeStatus::OK, status); }
 
   int count_frames_checked() const { return count_frames_checked_; }