Try disabling GPU watchdog in WebGL conformance tests.

It's believed that the flaky GPU process hangs seen on the waterfall
are spurious, not real. Try disabling the GPU watchdog. If the hangs
are real, this will result in test timeouts rather than GPU process
crashes, context loss, and test failures.

BUG=596622, 609252
CQ_INCLUDE_TRYBOTS=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;master.tryserver.chromium.android:android_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2446033002
Cr-Commit-Position: refs/heads/master@{#427247}

content/test/gpu/gpu_tests/webgl_conformance_integration_test.py

@@ -252,7 +252,11 @@ class WebGLConformanceIntegrationTest(gpu_integration_test.GpuIntegrationTest):
         '--disable-gpu-process-crash-limit',
         '--js-flags=--expose-gc',
         '--test-type=gpu',
-        '--enable-experimental-canvas-features'
+        '--enable-experimental-canvas-features',
+        # Try disabling the GPU watchdog to see if this affects the
+        # intermittent GPU process hangs that have been seen on the
+        # waterfall. crbug.com/596622 crbug.com/609252
+        '--disable-gpu-watchdog'
     ])
     if cls._webgl_version == 2:
       browser_options.AppendExtraBrowserArgs([