Add NavigationToFirstContentfulPaint UMA for ServiceWorker controlled pages.

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,
     WebLoadingBehaviorDocumentWriteEvaluator = 1 << 0,

[Bryan McQuade, 2016/04/14 15:10:26]

while here, can you add the comment
// Indicates that the page used the document.write evaluator to preload scan for
resources inserted via document.write.

[horo, 2016/04/14 15:46:31]

Done.

+    // Flag for a page that is controlled by a Service Worker.
+    WebLoadingBehaviorServiceWorkerControlled = 1 << 1,
 };
 
 } // namespace blink
 
 #endif // WebLoadingBehaviorFlag_h