Adds a CancellableTaskFactory and exposes postLoadingTasks to Blink

public/platform/WebScheduler.h

 // Copyright 2014 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 WebScheduler_h
 #define WebScheduler_h
 
 #include "WebCommon.h"
+#include "public/platform/WebThread.h"
 
 namespace blink {
 
 class WebTraceLocation;
 
 // This class is used to submit tasks and pass other information from Blink to
 // the platform's scheduler.
 class BLINK_PLATFORM_EXPORT WebScheduler {
 public:
     virtual ~WebScheduler() { }
@@ skipping 13 matching lines @@
     // Returns true if there is high priority work pending on the main thread
     // and the caller should yield to let the scheduler service that work.
     // Must be called on the main thread.
     virtual bool shouldYieldForHighPriorityWork() { return false; }
 
     // Schedule an idle task to run the Blink main thread. For non-critical
     // tasks which may be reordered relative to other task types and may be
     // starved for an arbitrarily long time if no idle time is available.
     // Takes ownership of |IdleTask|. Can be called from any thread.
     virtual void postIdleTask(const WebTraceLocation&, IdleTask*) { }
+
+    // Schedule a loading task to be run on the Blink main thread. Loading
+    // tasks usually have the default priority, but may be deprioritised
+    // when the user is interacting with the device.
+    // Takes ownership of |WebThread::Task|. Can be called from any thread.
+    virtual void postLoadingTask(const WebTraceLocation&, WebThread::Task*) { }
 };
 
 } // namespace blink
 
 #endif // WebScheduler_h