Don't crash after calling frame_->stopLoading().

content/renderer/render_frame_impl.cc

Index: content/renderer/render_frame_impl.cc
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
index 429c817d472f975d5f8113cf3f5b143d0f48ea20..c4ab0ba0599ab15f003bbf41bf5042a3671bf386 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -4500,7 +4500,7 @@ void RenderFrameImpl::RemoveObserver(RenderFrameObserver* observer) {
 void RenderFrameImpl::OnStop() {
   DCHECK(frame_);
   frame_->stopLoading();
-  if (!frame_->parent())
+  if (frame_ && !frame_->parent())
     FOR_EACH_OBSERVER(RenderViewObserver, render_view_->observers_, OnStop());
 
   FOR_EACH_OBSERVER(RenderFrameObserver, observers_, OnStop());
@@ -5653,7 +5653,7 @@ void RenderFrameImpl::NavigateInternal(
     // send a stop message if the HistoryController is loading in this frame
     // nonetheless. This behavior will go away with subframe navigation
     // entries.
-    if (!frame_->isLoading() && !has_history_navigation_in_frame)
+    if (frame_ && !frame_->isLoading() && !has_history_navigation_in_frame)
       Send(new FrameHostMsg_DidStopLoading(routing_id_));
   }