Ensure that child FrameTreeNodes are deleted after a navigation or crash.

content/browser/renderer_host/render_view_host_impl.cc

Index: content/browser/renderer_host/render_view_host_impl.cc
diff --git a/content/browser/renderer_host/render_view_host_impl.cc b/content/browser/renderer_host/render_view_host_impl.cc
index 2cfbc4078dfd1e2c5204e0b452a6dd845847b8c6..3858f7e9b1d5ae8ab7ce8caa8dc166b73a5ed671 100644
--- a/content/browser/renderer_host/render_view_host_impl.cc
+++ b/content/browser/renderer_host/render_view_host_impl.cc
@@ -1388,8 +1388,11 @@ void RenderViewHostImpl::OnRenderProcessGone(int status, int exit_code) {
   render_view_termination_status_ =
       static_cast<base::TerminationStatus>(status);
 
-  // Reset state.
+  // Reset frame tree state.
+  // TODO(creis): Once subframes can be in different processes, we'll need to
+  // clear just the FrameTreeNodes affected by the crash (and their subtrees).
   main_frame_id_ = -1;
+  delegate_->GetFrameTree()->SwapMainFrame(main_render_frame_host_.get());
 
   // Our base class RenderWidgetHost needs to reset some stuff.
   RendererExited(render_view_termination_status_, exit_code);