[Telemetry] Disable testWebviewInExtension on chromeos

telemetry/telemetry/internal/browser/extension_unittest.py

Index: telemetry/telemetry/internal/browser/extension_unittest.py
diff --git a/telemetry/telemetry/internal/browser/extension_unittest.py b/telemetry/telemetry/internal/browser/extension_unittest.py
index 8f551c8ec24078d5813ff810bb61a7c4d5b39426..514f2a5d95c4a19809f2233f056b870bc047bfaf 100644
--- a/telemetry/telemetry/internal/browser/extension_unittest.py
+++ b/telemetry/telemetry/internal/browser/extension_unittest.py
@@ -167,7 +167,8 @@ class WebviewInExtensionTest(ExtensionTest):
 
   # Flaky on windows, hits an exception: http://crbug.com/508325
   # Flaky on macOS too: http://crbug.com/661434
-  @decorators.Disabled('win', 'linux', 'mac')
+  # ChromeOS: http://crbug.com/674220
+  @decorators.Disabled('win', 'linux', 'mac', 'chromeos')
   def testWebviewInExtension(self):
     """Tests GetWebviewContext() for a web app containing <webview> element."""
     if not self.CreateBrowserWithExtension('webview_app'):