Mark WebglConformance tests as flaky on Android.

Three video related tests are failing flakily on the Android FYI
trybots. Failures have been seen on Nexus 9 and Nvidia Shield primarily,
so will set them flaky for nvidia boards.

TBR: kbr@chromium.org
Bug: 891456
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: I64d768be4cabf246b6e0ab007c87c2292a8adf42
Reviewed-on: https://chromium-review.googlesource.com/c/1263037Reviewed-by: kylechar <kylechar@chromium.org>
Commit-Queue: kylechar <kylechar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597155}

content/test/gpu/gpu_tests/webgl_conformance_expectations.py

@@ -724,6 +724,11 @@ class WebGLConformanceExpectations(GpuTestExpectations):
     self.Flaky('conformance/textures/misc/' +
         'tex-video-using-tex-unit-non-zero.html',
         ['android', 'nvidia'], bug=830901)
+    self.Flaky('conformance/extensions/oes-texture-half-float-with-video.html',
+        ['android', 'nvidia'], bug=891456)
+    self.Flaky('conformance/textures/image_bitmap_from_video/' +
+        'tex-2d-rgb-rgb-unsigned_short_5_6_5.html', ['android', 'nvidia'],
+        bug=891456)
 
     # Nexus 9 and Shield TV (NVIDIA GPUs currently on the waterfall)
     self.Fail('conformance/ogles/GL/array/array_001_to_006.html',