Mark tests flaky only on Mac10.10

crrev.com/c/1124729 marks a few tests as flaky on Mac, but this replaces it to
Mac10.10, which is more restrictive.

TBR=pdr@chromium.org
NOTRY=true

Bug: 857501
Change-Id: Ibca47cd41a2ec17b95372ea115081f08312217ba
Reviewed-on: https://chromium-review.googlesource.com/1124731Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572421}

third_party/WebKit/LayoutTests/TestExpectations

@@ -95,10 +95,9 @@ crbug.com/816045 [ Win Linux Mac ] virtual/gpu/fast/canvas/canvas-imageSmoothing
 # seem to fix it.
 crbug.com/309675 compositing/gestures/gesture-tapHighlight-simple-longPress.html [ Failure ]
 
-# These are failing only on Mac10.10 Tests bot.
-crbug.com/857501 [ Mac ] compositing/gestures/gesture-tapHighlight-pixel-rotated-div.html [ Failure Pass ]
-crbug.com/857501 [ Mac ] compositing/gestures/gesture-tapHighlight-pixel-rotated-link.html [ Failure Pass ]
-crbug.com/857501 [ Mac ] compositing/gestures/gesture-tapHighlight-pixel-transparent.html [ Failure Pass ]
+crbug.com/857501 [ Mac10.10 ] compositing/gestures/gesture-tapHighlight-pixel-rotated-div.html [ Failure Pass ]
+crbug.com/857501 [ Mac10.10 ] compositing/gestures/gesture-tapHighlight-pixel-rotated-link.html [ Failure Pass ]
+crbug.com/857501 [ Mac10.10 ] compositing/gestures/gesture-tapHighlight-pixel-transparent.html [ Failure Pass ]
 
 crbug.com/845267 [ Mac ] http/tests/inspector-protocol/page/page-lifecycleEvents.js [ Failure Pass ]