Skip WebglConformance_conformance_textures_video_tex_2d_rgb_rgb_unsigned_short_5_6_5

This is flaky on Nexus 9.  However, due to the existing webview skip,
there's not a way to mark this as non-webview flaky + webview skip.
So, just mark it as skipped with a comment.

Bug: 834933,928585
Change-Id: I39a72c28a9c76f2ef722fa225e38ad14b400ffa7
Reviewed-on: https://chromium-review.googlesource.com/c/1453803
Commit-Queue: enne <enne@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Auto-Submit: enne <enne@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629031}

content/test/gpu/gpu_tests/webgl_conformance_expectations.py

@@ -647,9 +647,10 @@ class WebGLConformanceExpectations(GpuTestExpectations):
     self.Skip('conformance/textures/video/' +
         'tex-2d-rgb-rgb-unsigned_byte.html',
         ['android', 'android-webview-instrumentation'], bug=352645)
+    # Also flaky on nexus9 non-webview (bug=834933) but can't specify both.
     self.Skip('conformance/textures/video/' +
         'tex-2d-rgb-rgb-unsigned_short_5_6_5.html',
-        ['android', 'android-webview-instrumentation'], bug=352645)
+        ['android'], bug=352645)
     self.Skip('conformance/textures/video/' +
         'tex-2d-rgba-rgba-unsigned_byte.html',
         ['android', 'android-webview-instrumentation'], bug=352645)