[Media Controls] Try minimizing volume slider layout test timeout

Change-Id: I390ffca8cb3273fc6e475695a3eeceb6324f741d
Reviewed-on: https://chromium-review.googlesource.com/c/1354649
Commit-Queue: Jazz Xu <jazzhsu@chromium.org>
Reviewed-by: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612430}

third_party/blink/web_tests/media/media-controls.js

@@ -428,9 +428,8 @@ function runAfterDoubleTapTimerFired(func) {
 }
 
 function hoverMuteButton(video, func) {
-  // 150ms slack because the test could be flaky on Mac Test build
-  // even with volume slider delay set to 0ms
-  const delayedCallback = function() { setTimeout(func, 150); };
+  // Wait for hover timer fires
+  const delayedCallback = function() { setTimeout(func); };
   const muteBtn = muteButton(video);
   hoverOverControl(muteBtn, delayedCallback);
 }