Allow passing mock FrameLoaderClient to DummyPageHolder.

Source/core/loader/EmptyClients.h

Index: Source/core/loader/EmptyClients.h
diff --git a/Source/core/loader/EmptyClients.h b/Source/core/loader/EmptyClients.h
index 3b29ec8b4c49c9a3b1d7d674b27d8be9b1c02f51..13fcee0861ea3019ec3ce52e58afad79601257c6 100644
--- a/Source/core/loader/EmptyClients.h
+++ b/Source/core/loader/EmptyClients.h
@@ -162,7 +162,7 @@ public:
     virtual String acceptLanguages() OVERRIDE;
 };
 
-class EmptyFrameLoaderClient FINAL : public FrameLoaderClient {
+class EmptyFrameLoaderClient : public FrameLoaderClient {
     WTF_MAKE_NONCOPYABLE(EmptyFrameLoaderClient); WTF_MAKE_FAST_ALLOCATED;
 public:
     EmptyFrameLoaderClient() { }