Correctly disable MirroringNothingWithTargetChange

The current code has a type, it should be DISABLED_xxx

TBR=wjmaclean@chromium.org
NOTRY=true

Bug: 872340
Change-Id: I910b6913eace9b4710a7aac990d783f0f842beee
Reviewed-on: https://chromium-review.googlesource.com/1176176Reviewed-by: Xida Chen <xidachen@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583321}

content/browser/media/capture/web_contents_audio_input_stream_unittest.cc

@@ -473,7 +473,7 @@ TEST_P(WebContentsAudioInputStreamTest, MirroringOutputWithinSession) {
 
 // TODO(https://crbug.com/872340): Test appears to have timing-dependent flake.
 TEST_P(WebContentsAudioInputStreamTest,
-       DISABLE_MirroringNothingWithTargetChange) {
+       DISABLED_MirroringNothingWithTargetChange) {
   RUN_ON_AUDIO_THREAD(Open);
   RUN_ON_AUDIO_THREAD(Start);
   RUN_ON_AUDIO_THREAD(ChangeMirroringTarget);