Add terminateServiceWorker method for layout tests - blink side

public/platform/WebServiceWorker.h

Index: public/platform/WebServiceWorker.h
diff --git a/public/platform/WebServiceWorker.h b/public/platform/WebServiceWorker.h
index 52ad440463796cc4c865bee1001d530c5a31e237..cfa834a3486c305197fc670d443aa7ee2b9ebe82 100644
--- a/public/platform/WebServiceWorker.h
+++ b/public/platform/WebServiceWorker.h
@@ -65,6 +65,8 @@ public:
     // Callee receives ownership of the passed vector.
     // FIXME: Blob refs should be passed to maintain ref counts. crbug.com/351753
     virtual void postMessage(const WebString&, WebMessagePortChannelArray*) { BLINK_ASSERT_NOT_REACHED(); }
+
+    virtual void terminate() { }
 };
 
 }