Skip three flaking GPU tests on Nexus 5X bots.

  ContextLost_WebGLBlockedAfterJSNavigation
  ContextLost_WebGLUnblockedAfterUserInitiatedReload
  TraceTest_Video_Context_Loss_VP9

These three tests are flaking frequently, and despite two of them
being marked flaky, their failures are showing up often enough in the
data that they're ranked highly on FindIt's flake portal. Skip them
entirely on this configuration.

Bug: 965268
Bug: 965730
Change-Id: Id1b3efe3577d348d0c04fc20a847f9b40a98c046
Tbr: ynovikov@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1628391Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662949}

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

@@ -34,7 +34,8 @@ crbug.com/609629 [ android ] ContextLost_WebGLContextLostFromGPUProcessExit [ Sk
 crbug.com/609629 [ android ] ContextLost_WebGLContextLostInHiddenTab [ Skip ]
 
 # Flaking on Nexus 5X
-crbug.com/879423 [ android qualcomm-adreno-(tm)-418 ] ContextLost_WebGLUnblockedAfterUserInitiatedReload [ RetryOnFailure ]
+crbug.com/965268 [ android qualcomm-adreno-(tm)-418 ] ContextLost_WebGLBlockedAfterJSNavigation [ Skip ]
+crbug.com/965268 [ android qualcomm-adreno-(tm)-418 ] ContextLost_WebGLUnblockedAfterUserInitiatedReload [ Skip ]
 crbug.com/880078 [ android ] ContextLost_WorkerRAFAfterGPUCrash [ Failure ]
 crbug.com/880078 [ android ] ContextLost_WorkerRAFAfterGPUCrash_OOPD [ Failure ]
 

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

@@ -33,4 +33,4 @@ crbug.com/937545 [ win10 nvidia ] VideoPathTraceTest_DirectComposition_ComplexOv
 
 # Flaky for unknown reason.
 crbug.com/960007 [ win10 nvidia ] OverlayModeTraceTest_DirectComposition_Nonroot [ RetryOnFailure ]
-crbug.com/965730 [ android qualcomm-adreno-(tm)-418 ] TraceTest_Video_Context_Loss_VP9 [ RetryOnFailure ]
+crbug.com/965730 [ android qualcomm-adreno-(tm)-418 ] TraceTest_Video_Context_Loss_VP9 [ Skip ]