Convert app banners to use Mojo.

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();
+};