With --site-per-process, avoid a crash when a subframe process goes away.

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 1c508907f62f0e12fbe356607055b6d067d7849f..cdf95d57a328a5cd8e2b29bce5a2293c3ca4b3b8 100644
--- a/content/browser/renderer_host/render_view_host_impl.cc
+++ b/content/browser/renderer_host/render_view_host_impl.cc
@@ -1431,11 +1431,9 @@ void RenderViewHostImpl::OnRenderProcessGone(int status, int exit_code) {
   render_view_termination_status_ =
       static_cast<base::TerminationStatus>(status);
 
-  // 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).
+  // Reset frame tree state associated with this process.
   main_frame_id_ = -1;
-  delegate_->GetFrameTree()->ResetForMainFrameSwap();
+  delegate_->GetFrameTree()->RenderProcessGone(this);
 
   // Our base class RenderWidgetHost needs to reset some stuff.
   RendererExited(render_view_termination_status_, exit_code);