Give the main frame a RenderWidget.

content/browser/frame_host/render_frame_host_manager.cc

Index: content/browser/frame_host/render_frame_host_manager.cc
diff --git a/content/browser/frame_host/render_frame_host_manager.cc b/content/browser/frame_host/render_frame_host_manager.cc
index 71ec817e8d78b47bf48cc58b0cf878138f5921cd..a144c38933779448eba353f3cab24d12c72006aa 100644
--- a/content/browser/frame_host/render_frame_host_manager.cc
+++ b/content/browser/frame_host/render_frame_host_manager.cc
@@ -254,18 +254,12 @@ RenderFrameHostManager::~RenderFrameHostManager() {
   SetRenderFrameHost(scoped_ptr<RenderFrameHostImpl>());
 }
 
-void RenderFrameHostManager::Init(BrowserContext* browser_context,
-                                  SiteInstance* site_instance,
+void RenderFrameHostManager::Init(SiteInstance* site_instance,
                                   int32 view_routing_id,
                                   int32 frame_routing_id,
                                   int32 widget_routing_id,
                                   int32 surface_id) {
-  // Create a RenderViewHost and RenderFrameHost, once we have an instance.  It
-  // is important to immediately give this SiteInstance to a RenderViewHost so
-  // that the SiteInstance is ref counted.
-  if (!site_instance)
-    site_instance = SiteInstance::Create(browser_context);
-
+  DCHECK(site_instance);
   int flags = delegate_->IsHidden() ? CREATE_RF_HIDDEN : 0;
   SetRenderFrameHost(CreateRenderFrameHost(site_instance, view_routing_id,
                                            frame_routing_id, widget_routing_id,
@@ -1741,12 +1735,13 @@ scoped_ptr<RenderFrameHostImpl> RenderFrameHostManager::CreateRenderFrame(
 
     int32 widget_routing_id = MSG_ROUTING_NONE;
     int32 surface_id = 0;
-    // A RenderFrame in a different process from its parent RenderFrame
-    // requires a RenderWidget for input/layout/painting.
-    if (frame_tree_node_->parent() &&
+    // A main RenderFrame, or a RenderFrame in a different process from its
+    // parent RenderFrame requires a RenderWidget for input/layout/painting.
+    if (!frame_tree_node_->parent() ||
         frame_tree_node_->parent()->current_frame_host()->GetSiteInstance() !=
             instance) {
-      CHECK(SiteIsolationPolicy::AreCrossProcessFramesPossible());
+      CHECK(!frame_tree_node_->parent() ||
+            SiteIsolationPolicy::AreCrossProcessFramesPossible());
       widget_routing_id = instance->GetProcess()->GetNextRoutingID();
       surface_id = GpuSurfaceTracker::Get()->AddSurfaceForRenderer(
           instance->GetProcess()->GetID(), widget_routing_id);