Cleanup: Add more conversion helpers for usage.

Source/web/ChromeClientImpl.h

Index: Source/web/ChromeClientImpl.h
diff --git a/Source/web/ChromeClientImpl.h b/Source/web/ChromeClientImpl.h
index 1a1e9965258cef52bb52f5dcf3ad9838d1f92bdd..9f59643e8b42f9a83fb688c8c8b7fad5a828f9e2 100644
--- a/Source/web/ChromeClientImpl.h
+++ b/Source/web/ChromeClientImpl.h
@@ -217,6 +217,14 @@ private:
 };
 #endif
 
+inline ChromeClientImpl* toChromeClientImpl(WebCore::ChromeClient* client)
+{
+    // 1. The client returned by Page::client() is a reference, hence never null.
+    // 2. There is no other class derived from ChromeClient other than ChromeClientImpl.

[tkent, 2013/10/08 05:24:04]

It's incorrect. AFAIK, we have EmptyChromeClient, PagePopupChromeClient,
HelperPluginChromeClient.

+    // Hence, we don't need ASSERT here to check for either of the conditions.
+    return static_cast<ChromeClientImpl*>(client);
+}
+
 } // namespace WebKit
 
 #endif