Suppress flaky screenshot test.

This is flaking on Viz/Windows/Intel. Not clear how to select viz
as a config in the GPU expectations module. Suppress this on the
Windows Intel config for now.

Bug: 853762
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: I83bc2699d7b7a904eb68b97886d1c91025307d31
Tbr: kbr@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/1104783Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568094}

content/test/gpu/gpu_tests/screenshot_sync_expectations.py

@@ -21,3 +21,6 @@ class ScreenshotSyncExpectations(GpuTestExpectations):
                bug=639489)
     # TODO(kbr): flakily timing out on this configuration.
     self.Flaky('*', ['linux', 'intel', 'debug'], bug=648369)
+    # This is only flaky on the Viz config. Unsure how to filter for viz.
+    self.Flaky('ScreenshotSync_GPURasterWithCanvas', ['win', 'intel'],
+               bug=853762)