gpu: Skip Pixel_OffscreenCanvasWebGLDefault test on Nexus 5X

This test is flaking too frequently to keep as RetryOnFailure.

TBR=kbr@chromium.org
BUG=1157136

Change-Id: I7bf819129c7136a7057eaeafaa60a9812c90fc91
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2643763
Auto-Submit: Victor Miura <vmiura@chromium.org>
Reviewed-by: Victor Miura <vmiura@chromium.org>
Commit-Queue: Victor Miura <vmiura@chromium.org>
Cr-Commit-Position: refs/heads/master@{#846443}

content/test/gpu/gpu_tests/test_expectations/pixel_expectations.txt

@@ -177,7 +177,10 @@ crbug.com/1029389 [ android android-nexus-5 ] Pixel_PrecisionRoundedCorner [ Ski
 crbug.com/883500 [ android-chromium android-nexus-5x ] Pixel_BackgroundImage [ RetryOnFailure ]
 crbug.com/1065514 [ android android-chromium android-nexus-5x ] Pixel_WebGLReadPixelsTabSwitch [ RetryOnFailure ]
 crbug.com/1121476 [ android android-chromium android-nexus-5x ] Pixel_Canvas2DTabSwitch [ RetryOnFailure ]
-crbug.com/1157136 [ android android-chromium android-nexus-5x skia-renderer-disabled ] Pixel_OffscreenCanvasWebGLDefault [ RetryOnFailure ]
+
+# Frequently fails on Nexus 5X
+crbug.com/1157136 [ android android-chromium android-nexus-5x skia-renderer-disabled ] Pixel_OffscreenCanvasWebGLDefault [ Skip ]
+crbug.com/1157136 [ android android-chromium android-nexus-5x skia-renderer-gl ] Pixel_OffscreenCanvasWebGLDefault [ Skip ]
 
 # We do not have software H.264 decoding on Android, so it can't survive a
 # context loss which results in hardware decoder loss.