MainFrameObserver is inline owned, so it shouldn't be freed by OnDestruct

content/renderer/web_ui_mojo.cc

Index: content/renderer/web_ui_mojo.cc
diff --git a/content/renderer/web_ui_mojo.cc b/content/renderer/web_ui_mojo.cc
index cb0207596818e880f30022d95a7feba8ff680ee5..aab0af22ce4273dd88ec1b594d74a6aca3d6d537 100644
--- a/content/renderer/web_ui_mojo.cc
+++ b/content/renderer/web_ui_mojo.cc
@@ -45,6 +45,9 @@ void WebUIMojo::MainFrameObserver::DidFinishDocumentLoad() {
   web_ui_mojo_->OnDidFinishDocumentLoad();
 }
 
+void WebUIMojo::MainFrameObserver::OnDestruct() {
+}
+
 WebUIMojo::WebUIMojo(RenderView* render_view)
     : RenderViewObserver(render_view),
       RenderViewObserverTracker<WebUIMojo>(render_view),