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 551327fc999ab6b2a3bc1b2838c9ab23d3e348dc..e5d13ca49acd6011d96a30a25ed4f27632858a52 100644
--- a/public/platform/WebScheduler.h
+++ b/public/platform/WebScheduler.h
@@ -57,6 +57,12 @@ 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*) { }
+
+    // Schedule a timer task to be run on the Blink main thread. Timer Tasks
+    // tasks usually have the default priority, but may be delayed
+    // when the user is interacting with the device.
+    // Takes ownership of |WebThread::Task|. Can be called from any thread.
+    virtual void postTimerTask(const WebTraceLocation&, WebThread::Task*, long long delayMs) { }
 };
 
 } // namespace blink