Implement "appinstalled" event on Android.

chrome/browser/banners/app_banner_manager.h

Index: chrome/browser/banners/app_banner_manager.h
diff --git a/chrome/browser/banners/app_banner_manager.h b/chrome/browser/banners/app_banner_manager.h
index 15bb380e82d3f31cb699af498d128748e08402fb..06fba428c46910f7012177c1afba35247b7efc8b 100644
--- a/chrome/browser/banners/app_banner_manager.h
+++ b/chrome/browser/banners/app_banner_manager.h
@@ -68,6 +68,11 @@ class AppBannerManager : public content::WebContentsObserver,
   // pipeline will be reported to the devtools console.
   virtual void RequestAppBanner(const GURL& validated_url, bool is_debug_mode);
 
+  // Informs the page that it has been installed via an app banner.
+  // This is redundant for the beforeinstallprompt event's promise being
+  // resolved, but is required by the install event spec.
+  void OnInstall();
+
   // Sends a message to the renderer that the user accepted the banner. Does
   // nothing if |request_id| does not match the current request.
   void SendBannerAccepted(int request_id);