update directcomposition Pixel_Video_VP9 revision

Bug: 754986
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: I234a2cc037b78b11d08660b641f5524ed8171a0b
Reviewed-on: https://chromium-review.googlesource.com/1014601Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551510}

content/test/gpu/gpu_tests/pixel_test_pages.py

@@ -701,6 +701,6 @@ def DirectCompositionPages(base_name):
       'pixel_video_vp9.html',
       base_name + '_DirectComposition_Video_VP9',
       test_rect=[0, 0, 300, 300],
-      revision=8,
+      revision=9,
       browser_args=browser_args),
   ]