Refactor TimeBase to post tasks. Workers to use real Idle tasks.

public/platform/WebScheduler.h

Index: public/platform/WebScheduler.h
diff --git a/public/platform/WebScheduler.h b/public/platform/WebScheduler.h
index 463d1300af735ada6a105b97c63716c5c66145e6..0110aeed885230e13c7098363f46b4ae58709f56 100644
--- a/public/platform/WebScheduler.h
+++ b/public/platform/WebScheduler.h
@@ -64,10 +64,18 @@ public:
     // Takes ownership of |WebThread::Task|. Can be called from any thread.
     virtual void postTimerTask(const WebTraceLocation&, WebThread::Task*, long long delayMs) { }
 
+    // Schedule a shutdown task to be run on the the associated WebThread. Shutdown
+    // tasks can run at any time, including after preShutdown has been called.
+    // Takes ownership of |WebThread::Task|. Can be called from any thread.
+    virtual void postShutdownTask(const WebTraceLocation&, WebThread::Task*, long long delayMs) { }
+
+    // Prevents execution of all tasks posted vis this interface, except shutdown tasks.
+    virtual void preShutdown() { }
+
 #ifdef INSIDE_BLINK
     // Helpers for posting bound functions as tasks.
-    typedef Function<void(double deadlineSeconds)> IdleTask;
-    typedef Function<void()> Task;
+    typedef WTF::Function<void(double deadlineSeconds)> IdleTask;
+    typedef WTF::Function<void()> Task;
 
     void postIdleTask(const WebTraceLocation&, PassOwnPtr<IdleTask>);
     void postNonNestableIdleTask(const WebTraceLocation&, PassOwnPtr<IdleTask>);