PlzNavigate: Fix crash when loading unreachable URL.

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 cb9e3d3faa5df2dc38de129057f07c3d243797bb..3caacd59e87fb6dbbf5ccf9a984bc134867d7eb3 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -4878,9 +4878,11 @@ void RenderFrameImpl::OnFailedNavigation(
       frame_->isViewSourceModeEnabled());
   SendFailedProvisionalLoad(failed_request, error, frame_);
 
-  // This check should have been done on the browser side already.
   if (!ShouldDisplayErrorPageForFailedLoad(error_code, common_params.url)) {
-    NOTREACHED();
+    // The browser expects this frame to be loading an error page. Inform it
+    // that the load stopped.
+    if (!frame_->isLoading())
+      Send(new FrameHostMsg_DidStopLoading(routing_id_));
     return;
   }