Change beforeinstallprompt event to take an array of platforms.

Source/modules/app_banner/AppBannerController.h

 // Copyright 2015 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.
 
 #ifndef AppBannerController_h
 #define AppBannerController_h
 
 namespace blink {
 
 enum class WebAppBannerPromptReply;
 class LocalFrame;
 class WebString;
+template <typename T> class WebVector;
 
 // FIXME: unless userChoice ends up implemented, this class should not exist and
 // a regular static method could be used instead.
 class AppBannerController final {
 public:
-    static void willShowInstallBannerPrompt(LocalFrame*, const WebString& platform, WebAppBannerPromptReply*);
+    static void willShowInstallBannerPrompt(LocalFrame*, const WebVector<WebString>& platforms, WebAppBannerPromptReply*);
 
 private:
     AppBannerController() = delete;
     ~AppBannerController() = delete;
 };
 
 } // namespace blink
 
 #endif // AppBannerController_h