Mark media/controls/video-controls-with-cast-rendering.html as flaky

The test has been marked as flaky on Mac and Windows, but it's flaky on
Linux too. Marge the entries.

Bug: 824775
Change-Id: I13e270b3583abcba2f8db6527c8f9305f33b3c47
Tbr: tguilbert@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2212016Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771455}

third_party/blink/web_tests/TestExpectations

@@ -4521,8 +4521,7 @@ crbug.com/851363 http/tests/devtools/sxg/sxg-prefetch-fail.js [ Pass Failure ]
 crbug.com/851363 http/tests/devtools/sxg/sxg-prefetch.js [ Pass Failure ]
 
 # Sheriff 2018-03-22
-crbug.com/824775 [ Win ] media/controls/video-controls-with-cast-rendering.html [ Pass Failure ]
-crbug.com/824775 [ Mac ] media/controls/video-controls-with-cast-rendering.html [ Pass Failure ]
+crbug.com/824775 media/controls/video-controls-with-cast-rendering.html [ Pass Failure ]
 crbug.com/824848 [ Linux ] external/wpt/html/semantics/links/following-hyperlinks/activation-behavior.window.html [ Pass Failure ]
 crbug.com/824848 [ Mac ] external/wpt/html/semantics/links/following-hyperlinks/activation-behavior.window.html [ Pass Failure ]
 crbug.com/824848 [ Win ] external/wpt/html/semantics/links/following-hyperlinks/activation-behavior.window.html [ Pass Failure ]