Introduce Origin-Trial for Service Worker Navigation Preload

content/browser/service_worker/service_worker_version.h

 // Copyright 2013 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 CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_VERSION_H_
 #define CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_VERSION_H_
 
 #include <stdint.h>
 
 #include <functional>
@@ skipping 409 matching lines @@
   // mojom::ServiceWorkerEventDispatcher, once all simple events got dispatched
   // through mojo, OnSimpleEventResponse function could be removed.
   void OnSimpleEventFinished(int request_id,
                              ServiceWorkerStatusCode status,
                              base::Time dispatch_event_time);
 
   void NotifyMainScriptRequestHandlerCreated();
   void NotifyMainScriptJobCreated(
       ServiceWorkerContextRequestHandler::CreateJobStatus status);
 
+  // Returns true if the service worker should support Navigation Preload.
+  // There are three possible states:
+  //  - A: Navigation Preload related methods and attributes are available in JS
+  //       and work correctly.
+  //  - B: Navigation Preload related methods and attributes are available in
+  //       JS. But NavigationPreloadManager's enable, disable and setHeaderValue
+  //       methods always return a rejected promise. And FetchEvent's
+  //       preloadResponse attribute returns a promise which always resolve with
+  //       undefined.
+  //  - C: Navigation Preload related methods and attributes are not available
+  //       in JS.
+  // This method returns true only for A case.
+  // blink::OriginTrials::serviceWorkerNavigationPreloadEnabled() returns true
+  // for both A and B case.
+  //
+  //  * Origin Trial: Have an effective header.
+  //                                 Command line
+  //                             Default  Enable  Disabled
+  //                   Default      B       A        B
+  //      Field trial  Enabled      A       A        B
+  //                   Disabled     B       A        B
+  //
+  //  * Origin Trial: No header.
+  //                                 Command line
+  //                             Default  Enable  Disabled
+  //                   Default      C       A        C
+  //      Field trial  Enabled      C       A        C
+  //                   Disabled     C       A        C

[falken, 2017/01/13 03:43:41]

Great comment.

+  bool IsNavigationPreloadSupported() const;
+
  private:
   friend class base::RefCounted<ServiceWorkerVersion>;
   friend class ServiceWorkerMetrics;
   friend class ServiceWorkerReadFromCacheJobTest;
   friend class ServiceWorkerStallInStoppingTest;
   friend class ServiceWorkerURLRequestJobTest;
   friend class ServiceWorkerVersionBrowserTest;
   friend class ServiceWorkerVersionTest;
 
   FRIEND_TEST_ALL_PREFIXES(ServiceWorkerControlleeRequestHandlerTest,
@@ skipping 417 matching lines @@
 
   // At this point |this| can have been deleted, so don't do anything other
   // than returning.
 
   return true;
 }
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_VERSION_H_