Propagate a user gesture bit for beforeinstallprompt.prompt()

third_party/WebKit/public/platform/modules/app_banner/app_banner.mojom

 // Copyright 2016 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.
 
 module blink.mojom;
 
 enum AppBannerPromptReply {
   NONE,
   CANCEL,
 };
 
 interface AppBannerController {
   // The browser asks the renderer if the app banner should be shown.
   BannerPromptRequest(AppBannerService service, AppBannerEvent& event,
                       array<string> platform) =>
       (AppBannerPromptReply reply, string referrer);
 };
 
 interface AppBannerEvent {
   // The browser informs the renderer the response to the app banner.
   BannerAccepted(string platform);
   BannerDismissed();
 };
 
 interface AppBannerService {
   // The renderer asks the browser to display a previously offered app banner.
-  DisplayAppBanner();
+  DisplayAppBanner(bool user_gesture);
 };