Use InterstitialPage through a delegate interface instead of deriving from it.

chrome/renderer/chrome_render_view_observer.cc

Index: chrome/renderer/chrome_render_view_observer.cc
===================================================================
--- chrome/renderer/chrome_render_view_observer.cc	(revision 120576)
+++ chrome/renderer/chrome_render_view_observer.cc	(working copy)
@@ -263,7 +263,6 @@
     IPC_MESSAGE_HANDLER(ChromeViewMsg_GetFPS, OnGetFPS)
     IPC_MESSAGE_HANDLER(ChromeViewMsg_AddStrictSecurityHost,
                         OnAddStrictSecurityHost)
-    IPC_MESSAGE_HANDLER(ChromeViewMsg_SetAsInterstitial, OnSetAsInterstitial)
     IPC_MESSAGE_UNHANDLED(handled = false)
   IPC_END_MESSAGE_MAP()
 
@@ -361,10 +360,6 @@
   strict_security_hosts_.insert(host);
 }
 
-void ChromeRenderViewObserver::OnSetAsInterstitial() {
-  content_settings_->SetAsInterstitial();
-}
-
 void ChromeRenderViewObserver::Navigate(const GURL& url) {
   // Execute cache clear operations that were postponed until a navigation
   // event (including tab reload).