Update Pixel_Video_MP4 expectations

Fails on Nexus 5X, Flaky on Linux NVIDIA

BUG=819635,820240
TBR=kbr@chromium.org

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: Ie1daa75a8144d7bbcd314cba228fc528e6a4956a
Reviewed-on: https://chromium-review.googlesource.com/955959
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542019}

content/test/gpu/gpu_tests/pixel_expectations.py

@@ -56,6 +56,9 @@ class PixelExpectations(GpuTestExpectations):
     self.Flaky('*', ['linux', 'intel', 'debug'], bug=648369)
 
     self.Flaky('Pixel_Video_MP4', ['android', 'nvidia'], bug=716564)
+    self.Fail('Pixel_Video_MP4',
+        ['android', ('qualcomm', 'Adreno (TM) 418')], bug=820240)
+    self.Flaky('Pixel_Video_MP4', ['linux', 'nvidia'], bug=819635)
 
     # TODO(junov); validate new test results
     self.Fail('Pixel_CanvasLowLatency2D',