Revert of Change WokerThread to use a blink::WebThread.

public/platform/WebThread.h

Index: public/platform/WebThread.h
diff --git a/public/platform/WebThread.h b/public/platform/WebThread.h
index f1a47465730fe24cae3ffcdeb55a8a2151a09577..6bee10fbfebd929305b7c94031e4bf87e545f79b 100644
--- a/public/platform/WebThread.h
+++ b/public/platform/WebThread.h
@@ -68,12 +68,6 @@
     // Must be called when the WebThread is running.
     virtual void exitRunLoop() = 0;
 
-    // Delayed work is driven by a shared timer.
-    typedef void (*SharedTimerFunction)();
-    virtual void setSharedTimerFiredFunction(SharedTimerFunction) = 0;
-    virtual void setSharedTimerFireInterval(double) = 0;
-    virtual void stopSharedTimer() = 0;
-
     virtual ~WebThread() { }
 };