Show message when "Request app banner" on DevTools is clicked but not enabled.

chrome/browser/ui/browser.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/browser.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <string>
@@ skipping 164 matching lines @@
 #include "components/ui/zoom/zoom_controller.h"
 #include "components/web_modal/web_contents_modal_dialog_manager.h"
 #include "content/public/browser/devtools_agent_host.h"
 #include "content/public/browser/interstitial_page.h"
 #include "content/public/browser/invalidate_type.h"
 #include "content/public/browser/navigation_controller.h"
 #include "content/public/browser/navigation_entry.h"
 #include "content/public/browser/notification_details.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/plugin_service.h"
+#include "content/public/browser/render_frame_host.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/render_widget_host.h"
 #include "content/public/browser/render_widget_host_view.h"
 #include "content/public/browser/security_style_explanation.h"
 #include "content/public/browser/security_style_explanations.h"
 #include "content/public/browser/site_instance.h"
 #include "content/public/browser/user_metrics.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/common/content_switches.h"
@@ skipping 1253 matching lines @@
 }
 
 bool Browser::RequestAppBanner(content::WebContents* web_contents) {
   banners::AppBannerManagerDesktop* manager =
       banners::AppBannerManagerDesktop::FromWebContents(web_contents);
   if (manager) {
     manager->RequestAppBanner(web_contents->GetMainFrame(),
                               web_contents->GetLastCommittedURL(), true);
     return true;
   }
+
+  web_contents->GetMainFrame()->AddMessageToConsole(
+      content::CONSOLE_MESSAGE_LEVEL_DEBUG,
+      "App banners are currently disabled. Please check chrome://flags/#" +
+          std::string(switches::kEnableAddToShelf));
   return false;
 }
 
 bool Browser::IsMouseLocked() const {
   return exclusive_access_manager_->mouse_lock_controller()->IsMouseLocked();
 }
 
 void Browser::OnWindowDidShow() {
   if (window_has_shown_)
     return;
@@ skipping 1267 matching lines @@
   if (contents && !allow_js_access) {
     contents->web_contents()->GetController().LoadURL(
         target_url,
         content::Referrer(),
         ui::PAGE_TRANSITION_LINK,
         std::string());  // No extra headers.
   }
 
   return contents != NULL;
 }