Remove usage of RenderViewHost which aren't needed anymore.

BUG=304341

Review URL: https://codereview.chromium.org/902683002

Cr-Commit-Position: refs/heads/master@{#314648}

content/browser/frame_host/frame_tree.cc

@@ -302,8 +302,7 @@ RenderViewHostImpl* FrameTree::GetRenderViewHost(SiteInstance* site_instance) {
 
 void FrameTree::RegisterRenderFrameHost(
     RenderFrameHostImpl* render_frame_host) {
-  SiteInstance* site_instance =
-      render_frame_host->render_view_host()->GetSiteInstance();
+  SiteInstance* site_instance = render_frame_host->GetSiteInstance();
   RenderViewHostMap::iterator iter =
       render_view_host_map_.find(site_instance->GetId());
   CHECK(iter != render_view_host_map_.end());
@@ -313,8 +312,7 @@ void FrameTree::RegisterRenderFrameHost(
 
 void FrameTree::UnregisterRenderFrameHost(
     RenderFrameHostImpl* render_frame_host) {
-  SiteInstance* site_instance =
-      render_frame_host->render_view_host()->GetSiteInstance();
+  SiteInstance* site_instance = render_frame_host->GetSiteInstance();
   int32 site_instance_id = site_instance->GetId();
   RenderViewHostMap::iterator iter =
       render_view_host_map_.find(site_instance_id);

content/browser/frame_host/navigator_impl.cc

@@ -264,9 +264,7 @@ void NavigatorImpl::DidStartProvisionalLoad(
                                              true /* is_renderer_initiated */,
                                              std::string(),
                                              controller_->GetBrowserContext()));
-      entry->set_site_instance(
-          static_cast<SiteInstanceImpl*>(
-              render_frame_host->render_view_host()->GetSiteInstance()));
+      entry->set_site_instance(render_frame_host->GetSiteInstance());
       // TODO(creis): If there's a pending entry already, find a safe way to
       // update it instead of replacing it and copying over things like this.
       if (pending_entry) {
@@ -552,8 +550,7 @@ void NavigatorImpl::DidNavigate(
   // assigning a site is not necessary for this URL.  In that case, the
   // SiteInstance can still be considered unused until a navigation to a real
   // page.
-  SiteInstanceImpl* site_instance =
-      static_cast<SiteInstanceImpl*>(render_frame_host->GetSiteInstance());
+  SiteInstanceImpl* site_instance = render_frame_host->GetSiteInstance();
   if (!site_instance->HasSite() &&
       ShouldAssignSiteForURL(params.url)) {
     site_instance->SetSite(params.url);