WebUI: Fix lifecycle-bug when RenderFrameHost is swapped out

content/browser/webui/web_ui_impl.h

Index: content/browser/webui/web_ui_impl.h
diff --git a/content/browser/webui/web_ui_impl.h b/content/browser/webui/web_ui_impl.h
index 268c7576e80e1bb3ee9ce5b38853f5035fbb986e..31857a533935328ef8ce7ed7d8b4747a9a42baae 100644
--- a/content/browser/webui/web_ui_impl.h
+++ b/content/browser/webui/web_ui_impl.h
@@ -36,6 +36,9 @@ class CONTENT_EXPORT WebUIImpl : public WebUI,
   // Called when a RenderView is reused for the same WebUI type (i.e. reload).
   void RenderViewReused(RenderViewHost* render_view_host, bool was_main_frame);
 
+  // Called when the owning RenderFrameHost has started swapping out.
+  void RenderFrameHostSwappingOut();
+
   // WebUI implementation:
   WebContents* GetWebContents() const override;
   WebUIController* GetController() const override;