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..67aae44be37fd02ecd6be0485881253a188b910d 100644
--- a/media/cast/sender/h264_vt_encoder_unittest.cc
+++ b/media/cast/sender/h264_vt_encoder_unittest.cc
@@ -167,8 +167,8 @@ class EndToEndFrameChecker
     ++count_frames_checked_;
   }
 
-  void DecodeDone(VideoDecoder::Status status) {
-    EXPECT_EQ(VideoDecoder::kOk, status);
+  void DecodeDone(DecoderStatus status) {
+    EXPECT_EQ(DecoderStatus::OK, status);
   }
 
   int count_frames_checked() const { return count_frames_checked_; }