Cleanup: Adding more conversion helper interfaces.

Source/web/FrameLoaderClientImpl.h

Index: Source/web/FrameLoaderClientImpl.h
diff --git a/Source/web/FrameLoaderClientImpl.h b/Source/web/FrameLoaderClientImpl.h
index 945c8c38fa317bb3d993a806a927c1a09cab9665..4664dd29d99f1caff6ee34ec674bf423e8aa05ed 100644
--- a/Source/web/FrameLoaderClientImpl.h
+++ b/Source/web/FrameLoaderClientImpl.h
@@ -156,6 +156,8 @@ public:
     virtual void didStopAllLoaders() OVERRIDE;
 
 private:
+    virtual bool isFrameLoaderClientImpl() const OVERRIDE { return true; }
+
     PassOwnPtr<WebPluginLoadObserver> pluginLoadObserver();
 
     // The WebFrame that owns this object and manages its lifetime. Therefore,
@@ -163,6 +165,12 @@ private:
     WebFrameImpl* m_webFrame;
 };
 
+inline FrameLoaderClientImpl* toFrameLoaderClientImpl(WebCore::FrameLoaderClient* client)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!client || client->isFrameLoaderClientImpl());
+    return static_cast<FrameLoaderClientImpl*>(client);
+}
+
 } // namespace WebKit
 
 #endif