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

Source/platform/WebThreadSupportingGC.h

Index: Source/platform/WebThreadSupportingGC.h
diff --git a/Source/platform/WebThreadSupportingGC.h b/Source/platform/WebThreadSupportingGC.h
index 5899cb748d182f8efb90e7cb73a2ba781b13ac4c..3eb4b44f2f7cd6ca2453edaa03e0b34ca9932d41 100644
--- a/Source/platform/WebThreadSupportingGC.h
+++ b/Source/platform/WebThreadSupportingGC.h
@@ -37,6 +37,16 @@ public:
         m_thread->postDelayedTask(location, task, delayMs);
     }
 
+    void postIdleTask(const WebTraceLocation& location, WebThread::IdleTask* idleTask)
+    {
+        m_thread->postIdleTask(location, idleTask);
+    }
+
+    void postIdleTaskAfterWakeup(const WebTraceLocation& location, WebThread::IdleTask* idleTask)
+    {
+        m_thread->postIdleTaskAfterWakeup(location, idleTask);
+    }
+
     bool isCurrentThread() const
     {
         return m_thread->isCurrentThread();