Remove remaining WebContentsImpl from InterstitialPageImpl.

content/public/browser/interstitial_page.cc

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/public/browser/interstitial_page.h"
+
+#include "content/browser/web_contents/interstitial_page_impl.h"
+#include "content/browser/web_contents/web_contents_impl.h"
+
+namespace content {
+
+InterstitialPage* InterstitialPage::Create(WebContents* web_contents,
+                                           bool new_navigation,
+                                           const GURL& url,
+                                           InterstitialPageDelegate* delegate) {
+  return new InterstitialPageImpl(
+      web_contents,
+      static_cast<RenderWidgetHostDelegate*>(
+          static_cast<WebContentsImpl*>(web_contents)),
+      new_navigation, url, delegate);
+}
+
+}  // namespace content