Add support for postNonNestableIdleTask to the Scheduler and use it in Oilpan

Source/platform/scheduler/Scheduler.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 Scheduler_h
 #define Scheduler_h
 
 #include "platform/PlatformExport.h"
 #include "public/platform/WebThread.h"
 #include "wtf/Functional.h"
@@ skipping 13 matching lines @@
     typedef Function<void(double deadlineSeconds)> IdleTask;
 
     static Scheduler* shared();
     static void setForTesting(Scheduler*);
     static void shutdown();
 
     // 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.
     void postIdleTask(const WebTraceLocation&, PassOwnPtr<IdleTask>);
 
+    // Like postIdleTask but guarantees that the posted task will not run
+    // nested within an already-running task. Posting an idle task as
+    // non-nestable may not affect when the task gets run, or it could
+    // make it run later than it normally would, but it won't make it
+    // run earlier than it normally would.
+    void postNonNestableIdleTask(const WebTraceLocation&, PassOwnPtr<IdleTask>);
+
     // Like postIdleTask but does not run the idle task until after some other
     // task has run. This enables posting of a task which won't stop the Blink
     // main thread from sleeping, but will start running after it wakes up.
     void postIdleTaskAfterWakeup(const WebTraceLocation&, PassOwnPtr<IdleTask>);
 
     // For tasks related to loading, e.g. HTML parsing.  Loading tasks usually have default priority
     // but they may be deprioritized when the user is interacting with the device.
     // Takes ownership of |WebThread::Task|.
     void postLoadingTask(const WebTraceLocation&, WebThread::Task*);
 
     // 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.
     bool shouldYieldForHighPriorityWork() const;
 
 protected:
     Scheduler(WebScheduler*);
     virtual ~Scheduler();
 
     static Scheduler* s_sharedScheduler;
     WebScheduler* m_webScheduler;
 };
 
 } // namespace blink
 
 #endif // Scheduler_h