Metrics for document.write script blocking

third_party/WebKit/public/platform/WebLoadingBehaviorFlag.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef WebLoadingBehaviorFlag_h
 #define WebLoadingBehaviorFlag_h
 
 namespace blink {
 
 // This enum tracks certain behavior Blink exhibits when loading a page. This is
 // for use in metrics collection by the loading team, to evaluate experimental
 // features and potential areas of improvement in the loading stack. The main
 // consumer is the page_load_metrics component, which sends bit flags to the
 // browser process for histogram splitting.
 enum WebLoadingBehaviorFlag {
     WebLoadingBehaviorNone = 0,
     // Indicates that the page used the document.write evaluator to preload scan for resources inserted via document.write.
     WebLoadingBehaviorDocumentWriteEvaluator = 1 << 0,
     // Indicates that the page is controlled by a Service Worker.
     WebLoadingBehaviorServiceWorkerControlled = 1 << 1,
+    // Indicates that the page has a synchronous, cross-origin document.written
+    // script.
+    WebLoadingBehaviorDocumentWriteBlock = 1 << 1,

[Charlie Harrison, 2016/04/29 13:37:53]

Looks like you are clobbering WebLoadingBehaviorServiceWorkerControlled (which
should probably have a test to ensure this never happens).

[shivanisha, 2016/04/29 15:42:36]

My bad. Thanks for catching this. 
I have added a test to check no two values are equal
(DocumentWritePageLoadMetricsObserverTest.ValidFeatureFlags). Only thing I am
concerned about is that  for the test to be extensible to new values , it needs
updation when someone adds a new value to the enum, else it will always pass for
the existing values. I have added a comment to do so.

+    // Indicates that the page is a reload and has a synchronous, cross-origin document.written
+    // script.
+    WebLoadingBehaviorDocumentWriteBlockReload = 1 << 2,
 };
 
 } // namespace blink
 
 #endif // WebLoadingBehaviorFlag_h