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

Source/core/workers/WorkerLoaderProxy.h

Index: Source/core/workers/WorkerLoaderProxy.h
diff --git a/Source/core/workers/WorkerLoaderProxy.h b/Source/core/workers/WorkerLoaderProxy.h
index f4b8c42bd4902d6e97dfd1618f711ad7a414ade4..b54d2e991981b4a380b824cb755a44c5d5b6d770 100644
--- a/Source/core/workers/WorkerLoaderProxy.h
+++ b/Source/core/workers/WorkerLoaderProxy.h
@@ -85,9 +85,11 @@ public:
     // required to call detachProvider() when finalizing.
     void detachProvider(WorkerLoaderProxyProvider*);
 
-private:
+protected:
+    // Protected for testing.
     explicit WorkerLoaderProxy(WorkerLoaderProxyProvider*);
 
+private:
     Mutex m_lock;
     WorkerLoaderProxyProvider* m_loaderProxyProvider;
 };