Devirtualize InterstitialPageImpl::CreateRenderViewHost

This isn't overridden by any tests, so make it a private method.

BUG=304341

Review URL: https://codereview.chromium.org/697163002

Cr-Commit-Position: refs/heads/master@{#302473}

content/browser/frame_host/interstitial_page_impl.cc

@@ -244,7 +244,7 @@ void InterstitialPageImpl::Show() {
   }
 
   DCHECK(!render_view_host_);
-  render_view_host_ = static_cast<RenderViewHostImpl*>(CreateRenderViewHost());
+  render_view_host_ = CreateRenderViewHost();
   render_view_host_->AttachToFrameTree();
   CreateWebContentsView();
 
@@ -553,7 +553,7 @@ WebContents* InterstitialPageImpl::web_contents() const {
   return web_contents_;
 }
 
-RenderViewHost* InterstitialPageImpl::CreateRenderViewHost() {
+RenderViewHostImpl* InterstitialPageImpl::CreateRenderViewHost() {
   if (!enabled())
     return NULL;
 

content/browser/frame_host/interstitial_page_impl.h

@@ -168,10 +168,6 @@ class CONTENT_EXPORT InterstitialPageImpl
   WebContents* web_contents() const;
   const GURL& url() const { return url_; }
 
-  // Creates the RenderViewHost containing the interstitial content.
-  // Overriden in unit tests.
-  virtual RenderViewHost* CreateRenderViewHost();
-
   // Creates the WebContentsView that shows the interstitial RVH.
   // Overriden in unit tests.
   virtual WebContentsView* CreateWebContentsView();
@@ -201,6 +197,9 @@ class CONTENT_EXPORT InterstitialPageImpl
   void OnDomOperationResponse(const std::string& json_string,
                               int automation_id);
 
+  // Creates the RenderViewHost containing the interstitial content.
+  RenderViewHostImpl* CreateRenderViewHost();
+
   // The contents in which we are displayed.  This is valid until Hide is
   // called, at which point it will be set to NULL because the WebContents
   // itself may be deleted.