Mark virtual/gpu/fast/canvas/canvas-blending-pattern-over-pattern.html as flaky timeout on Mac

Change-Id: I17dfd6ca8e94db3b610cca28e0feca2b63bb3d01
Tbr: xiaochengh@chromium.org
NoTry: True
Bug: 860706
Reviewed-on: https://chromium-review.googlesource.com/1139435Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575516}

third_party/WebKit/LayoutTests/TestExpectations

@@ -4629,4 +4629,5 @@ crbug.com/860706 [ Mac ] virtual/gpu/fast/canvas/canvas-blending-pattern-over-im
 crbug.com/860706 [ Mac ] virtual/gpu/fast/canvas/canvas-blending-image-over-image.html [ Timeout Pass ]
 crbug.com/860706 [ Mac ] virtual/gpu/fast/canvas/color-space/canvas-createImageBitmap-rec2020.html [ Timeout Pass ]
 crbug.com/860706 [ Mac ] virtual/gpu/fast/canvas/canvas-blending-color-over-pattern.html [ Timeout Pass ]
+crbug.com/860706 [ Mac ] virtual/gpu/fast/canvas/canvas-blending-pattern-over-pattern.html [ Timeout Pass ]
 crbug.com/860706 [ Mac ] virtual/gpu/fast/canvas/canvas-shadow-source-in.html [ Timeout Pass ]
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