scheduler: Add an unthrottled per-frame task runner

third_party/WebKit/public/platform/WebFrameScheduler.h

 // Copyright 2015 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 WebFrameScheduler_h
 #define WebFrameScheduler_h
 
 #include "WebCommon.h"
 
 #include <string>
@@ skipping 14 matching lines @@
     // The scheduler may throttle tasks associated with pages that are not visible.
     virtual void setPageVisible(bool) { }
 
     // Returns the WebTaskRunner for loading tasks.
     // WebFrameScheduler owns the returned WebTaskRunner.
     virtual WebTaskRunner* loadingTaskRunner() { return nullptr; }
 
     // Returns the WebTaskRunner for timer tasks.
     // WebFrameScheduler owns the returned WebTaskRunner.
     virtual WebTaskRunner* timerTaskRunner() { return nullptr; }
+
+    // Returns the WebTaskRunner for tasks which should never get throttled.
+    // This is generally used for executing internal browser tasks which should
+    // never be throttled. Ideally only tasks whose performance characteristics
+    // are known should be posted to this task runner; for example user
+    // JavaScript is discouraged. WebFrameScheduler owns the returned
+    // WebTaskRunner.
+    virtual WebTaskRunner* unthrottledTaskRunner() { return nullptr; }
 };
 
 } // namespace blink
 
 #endif // WebFrameScheduler_h