Revert "Disable flaky WebVrTransitionTest#testWindowRafStopsFiringWhilePresenting on Android"

This reverts commit 1f41d1da.

Reason for revert: These flakes are addressed with  https://chromium.googlesource.com/chromium/src.git/+/044cca4ad8bc7a80c6edbd4e8dd4d078fd5f7659

Original change's description:
> Disable flaky WebVrTransitionTest#testWindowRafStopsFiringWhilePresenting on Android
> 
> TBR=bsheedy@chromium.org
> 
> Bug: 840725
> Change-Id: Id47604a849bcfcbb51e33ddf94ffa7a539ecb1df
> Reviewed-on: https://chromium-review.googlesource.com/1049668
> Reviewed-by: Guido Urdaneta <guidou@chromium.org>
> Commit-Queue: Guido Urdaneta <guidou@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#556762}

TBR=guidou@chromium.org,bsheedy@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 840725
Change-Id: Ie558ae22bc52438a919ccf0a49d15bea6d2ab424
Reviewed-on: https://chromium-review.googlesource.com/1054350
Commit-Queue: Eric Karl <ericrk@chromium.org>
Reviewed-by: Eric Karl <ericrk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557661}

chrome/android/javatests/src/org/chromium/chrome/browser/vr_shell/WebVrTransitionTest.java

@@ -406,7 +406,6 @@ public class WebVrTransitionTest {
      */
     @Test
     @MediumTest
-    @DisabledTest(message = "crbug.com/840725")
     @VrActivityRestriction({VrActivityRestriction.SupportedActivity.ALL})
     @RetryOnFailure
     public void testWindowRafStopsFiringWhilePresenting() throws InterruptedException {