Add Skia Gold killswitch to GPU tests

Adds a --bypass-skia-gold-functionality flag to
skia_gold_integration_test_base.py which causes all tests to skip any
actual interaction with Gold.

This is meant to be used in the unlikely event that there's a Gold
outage that can't be fixed quickly so that the outage does not block
CLs, etc.

Bug: 1057848
Change-Id: I2e5e8d0bfc956fd701cc329d4628755612a02e9f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2123036
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Auto-Submit: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753828}

content/test/gpu/gpu_tests/skia_gold_integration_test_base.py

@@ -171,6 +171,12 @@ class SkiaGoldIntegrationTestBase(gpu_integration_test.GpuIntegrationTest):
       help='Don\'t use the service account provided by LUCI for authentication '
            'for Skia Gold, instead relying on gsutil to be pre-authenticated. '
            'Meant for testing locally instead of on the bots.')
+    parser.add_option(
+      '--bypass-skia-gold-functionality',
+      action='store_true', default=False,
+      help='Bypass all interaction with Skia Gold, effectively disabling the '
+           'image comparison portion of any tests that use Gold. Only meant to '
+           'be used in case a Gold outage occurs and cannot be fixed quickly.')
 
   @classmethod
   def ResetGpuInfo(cls):
@@ -375,6 +381,10 @@ class SkiaGoldIntegrationTestBase(gpu_integration_test.GpuIntegrationTest):
       page: the GPU PixelTestPage object for the test.
       build_id_args: a list of build-identifying flags and values.
     """
+    if self.GetParsedCommandLineOptions().bypass_skia_gold_functionality:
+      logging.warning('Not actually comparing with Gold due to '
+                      '--bypass-skia-gold-functionality being present.')
+      return
     if not isinstance(build_id_args, list) or '--commit' not in build_id_args:
       raise Exception('Requires build args to be specified, including --commit')