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

Source/platform/scheduler/Scheduler.h

Index: Source/platform/scheduler/Scheduler.h
diff --git a/Source/platform/scheduler/Scheduler.h b/Source/platform/scheduler/Scheduler.h
index a18621d0e3705e7d592434b7b4ad09e961158f18..3fcff34897b838dc44bed97b6b835cd74c7ba6c3 100644
--- a/Source/platform/scheduler/Scheduler.h
+++ b/Source/platform/scheduler/Scheduler.h
@@ -40,6 +40,8 @@ public:
     // Takes ownership of |WebThread::Task|.
     void postLoadingTask(const WebTraceLocation&, WebThread::Task*);
 
+    void postTimerTask(const WebTraceLocation&, WebThread::Task*, long long delayMs);
+
     // 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.