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 a2cda3eac91603b1f741794377d01c942d88d16e..2cb7390aba398af164c891271bead150044d9f0a 100644
--- a/public/platform/WebScheduler.h
+++ b/public/platform/WebScheduler.h
@@ -52,6 +52,8 @@ public:
     // 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*) { }
+
+    virtual void postTimerTask(const WebTraceLocation&, WebThread::Task*, long long delayMs) { }
 };
 
 } // namespace blink