Mark Pixel_Video_MP4 flaky on NVIDIA android.

It's currently flaking on the NVIDIA Shield TV.

BUG=716564
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

Review-Url: https://codereview.chromium.org/2850973002
Cr-Commit-Position: refs/heads/master@{#468191}

content/test/gpu/gpu_tests/pixel_expectations.py

@@ -42,6 +42,8 @@ class PixelExpectations(GpuTestExpectations):
     # TODO(kbr): flakily timing out on this configuration.
     self.Flaky('*', ['linux', 'intel', 'debug'], bug=648369)
 
+    self.Flaky('Pixel_Video_MP4', ['android', 'nvidia'], bug=716564)
+
     # Flaky for unknown reasons only on macOS. Not planning to investigate
     # further.
     self.Flaky('Pixel_ScissorTestWithPreserveDrawingBuffer', ['mac'],