Give the main frame a RenderWidget.

content/browser/frame_host/render_frame_host_impl.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/browser/frame_host/render_frame_host_impl.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/containers/hash_tables.h"
 #include "base/lazy_instance.h"
@@ skipping 196 matching lines @@
   } else {
     rfh_state_ = STATE_DEFAULT;
     GetSiteInstance()->increment_active_frame_count();
   }
 
   SetUpMojoIfNeeded();
   swapout_event_monitor_timeout_.reset(new TimeoutMonitor(base::Bind(
       &RenderFrameHostImpl::OnSwappedOut, weak_ptr_factory_.GetWeakPtr())));
 
   if (widget_routing_id != MSG_ROUTING_NONE) {
-    render_widget_host_ = new RenderWidgetHostImpl(rwh_delegate, GetProcess(),
-                                                   widget_routing_id, hidden);
-    render_widget_host_->set_owned_by_render_frame_host(true);
+    // TODO(avi): Once RenderViewHostImpl has-a RenderWidgetHostImpl, the main
+    // render frame should probably start owning the RenderWidgetHostImpl,
+    // so this logic checking for an already existing RWHI should be removed.
+    // https://crbug.com/545684
+    render_widget_host_ =
+        RenderWidgetHostImpl::FromID(GetProcess()->GetID(), widget_routing_id);
+    if (!render_widget_host_) {
+      render_widget_host_ = new RenderWidgetHostImpl(rwh_delegate, GetProcess(),
+                                                     widget_routing_id, hidden);
+      render_widget_host_->set_owned_by_render_frame_host(true);
+    }

[ncarter (slow), 2015/10/21 22:15:48]

Does it make sense to add a DCHECK:

else {
 DCHECK(!render_widget_host_->owned_by_render_frame_host()); 
}

The danger being that if that dcheck doesn't hold, we'd call shutdown on our
non-owned RWH in the dtor, which seems bad? This would be more for documentation
than correctness.

[dcheng, 2015/10/21 23:46:51]

Done.

   }
 }
 
 RenderFrameHostImpl::~RenderFrameHostImpl() {
   GetProcess()->RemoveRoute(routing_id_);
   g_routing_id_frame_map.Get().erase(
       RenderFrameHostID(GetProcess()->GetID(), routing_id_));
 
   if (delegate_ && render_frame_created_)
     delegate_->RenderFrameDeleted(this);
 
   // If this was swapped out, it already decremented the active frame count of
   // the SiteInstance it belongs to.
   if (IsRFHStateActive(rfh_state_))
     GetSiteInstance()->decrement_active_frame_count();
 
-  // Notify the FrameTree that this RFH is going away, allowing it to shut down
-  // the corresponding RenderViewHost if it is no longer needed.
-  frame_tree_->ReleaseRenderViewHostRef(render_view_host_);
-
   // NULL out the swapout timer; in crash dumps this member will be null only if
   // the dtor has run.
   swapout_event_monitor_timeout_.reset();
 
   for (const auto& iter: visual_state_callbacks_) {
     iter.second.Run(false);
   }
 
-  if (render_widget_host_) {
+  if (render_widget_host_ &&
+      render_widget_host_->owned_by_render_frame_host()) {
     // Shutdown causes the RenderWidgetHost to delete itself.
     render_widget_host_->Shutdown();
   }
+
+  // Notify the FrameTree that this RFH is going away, allowing it to shut down
+  // the corresponding RenderViewHost if it is no longer needed.
+  frame_tree_->ReleaseRenderViewHostRef(render_view_host_);
 }
 
 int RenderFrameHostImpl::GetRoutingID() {
   return routing_id_;
 }
 
 AXTreeIDRegistry::AXTreeID RenderFrameHostImpl::GetAXTreeID() {
   return AXTreeIDRegistry::GetInstance()->GetOrCreateAXTreeID(
       GetProcess()->GetID(), routing_id_);
 }
@@ skipping 685 matching lines @@
 void RenderFrameHostImpl::OnDidDropNavigation() {
   // At the end of Navigate(), the FrameTreeNode's DidStartLoading is called to
   // force the spinner to start, even if the renderer didn't yet begin the load.
   // If it turns out that the renderer dropped the navigation, the spinner needs
   // to be turned off.
   frame_tree_node_->DidStopLoading();
   navigation_handle_.reset();
 }
 
 RenderWidgetHostImpl* RenderFrameHostImpl::GetRenderWidgetHost() {
-  if (render_widget_host_)
-    return render_widget_host_;
-
-  // TODO(kenrb): Remove this fallback and have the top-level frame have a
-  // widget host just like all the other frames.
-  if (!GetParent())
-    return render_view_host_->GetWidget();
-
-  return nullptr;
+  return render_widget_host_;
 }
 
 RenderWidgetHostView* RenderFrameHostImpl::GetView() {
   RenderFrameHostImpl* frame = this;
   while (frame) {
     if (frame->render_widget_host_)
       return frame->render_widget_host_->GetView();
     frame = static_cast<RenderFrameHostImpl*>(frame->GetParent());
   }
 
-  return render_view_host_->GetWidget()->GetView();
+  NOTREACHED();
+  return nullptr;
 }
 
 int RenderFrameHostImpl::GetEnabledBindings() {
   return render_view_host_->GetEnabledBindings();
 }
 
 void RenderFrameHostImpl::SetNavigationHandle(
     scoped_ptr<NavigationHandleImpl> navigation_handle) {
   navigation_handle_ = navigation_handle.Pass();
 }
@@ skipping 1283 matching lines @@
             BrowserPluginInstanceIDToAXTreeID(value)));
         break;
       case AX_CONTENT_INT_ATTRIBUTE_LAST:
         NOTREACHED();
         break;
     }
   }
 }
 
 }  // namespace content