Cleanup: Adding more conversion helper interfaces.

Source/web/ChromeClientImpl.h

Index: Source/web/ChromeClientImpl.h
diff --git a/Source/web/ChromeClientImpl.h b/Source/web/ChromeClientImpl.h
index 1a1e9965258cef52bb52f5dcf3ad9838d1f92bdd..1307affd7408fab952df710fc2b65ef8a6759127 100644
--- a/Source/web/ChromeClientImpl.h
+++ b/Source/web/ChromeClientImpl.h
@@ -188,6 +188,8 @@ public:
     virtual void didAssociateFormControls(const Vector<RefPtr<WebCore::Element> >&) OVERRIDE;
 
 private:
+    virtual bool isChromeClientImpl() const OVERRIDE { return true; }
+
     WebNavigationPolicy getNavigationPolicy();
     void getPopupMenuInfo(WebCore::PopupContainer*, WebPopupMenuInfo*);
     void setCursor(const WebCursorInfo&);
@@ -217,6 +219,12 @@ private:
 };
 #endif
 
+inline ChromeClientImpl* toChromeClientImpl(WebCore::ChromeClient& client)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(client.isChromeClientImpl());
+    return static_cast<ChromeClientImpl*>(&client);
+}
+
 } // namespace WebKit
 
 #endif