WebUI: Add JavaScript lifecycle-control to WebUIMessageHandler.

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 a372a40e679bddecc3734ac33351dc3ca14b5b01..268c7576e80e1bb3ee9ce5b38853f5035fbb986e 100644
--- a/content/browser/webui/web_ui_impl.h
+++ b/content/browser/webui/web_ui_impl.h
@@ -55,6 +55,7 @@ class CONTENT_EXPORT WebUIImpl : public WebUI,
   void ProcessWebUIMessage(const GURL& source_url,
                            const std::string& message,
                            const base::ListValue& args) override;
+  bool CanCallJavascript() override;
   void CallJavascriptFunction(const std::string& function_name) override;
   void CallJavascriptFunction(const std::string& function_name,
                               const base::Value& arg) override;