Add BackGestureRouter interface

This is needed for CastContentWindow to receive
backgesture support notifications

Merge-With: eureka-internal/367600
Bug: Internal b/149740737
Test: Build cast_shell
Change-Id: Iacde9b0687106b1093572fa0b2f8339a2d7b5bf1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2071015Reviewed-by: Sean Topping <seantopping@chromium.org>
Reviewed-by: Ryan Daum <rdaum@chromium.org>
Commit-Queue: Shawn Gallea <sagallea@google.com>
Cr-Commit-Position: refs/heads/master@{#744791}

chromecast/browser/BUILD.gn

@@ -473,6 +473,7 @@ cast_source_set("public") {
   deps = [
     "//base",
     "//chromecast/graphics",
+    "//chromecast/ui:back_gesture_router",
     "//chromecast/ui/mojom",
     "//content/public/common",
     "//ui/events",

chromecast/browser/cast_content_window.h

@@ -14,6 +14,7 @@
 #include "base/observer_list_types.h"
 #include "chromecast/browser/cast_web_contents.h"
 #include "chromecast/graphics/gestures/cast_gesture_handler.h"
+#include "chromecast/ui/back_gesture_router.h"
 #include "chromecast/ui/mojom/media_control_ui.mojom.h"
 #include "chromecast/ui/mojom/ui_service.mojom.h"
 #include "ui/events/event.h"
@@ -216,6 +217,10 @@ class CastContentWindow {
   // Media control interface. Non-null on Aura platforms.
   virtual mojom::MediaControlUi* media_controls();
 
+  // Registers this as a delegate to BackGestureRouter.
+  virtual void RegisterBackGestureRouter(
+      ::chromecast::BackGestureRouter* gesture_router) {}
+
   // Observer interface:
   void AddObserver(Observer* observer);
   void RemoveObserver(Observer* observer);

chromecast/ui/BUILD.gn

@@ -92,3 +92,7 @@ static_library("vector_icons") {
     "//ui/gfx",
   ]
 }
+
+cast_source_set("back_gesture_router") {
+  sources = [ "back_gesture_router.h" ]
+}

chromecast/ui/back_gesture_router.h

+// Copyright 2019 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 CHROMECAST_UI_BACK_GESTURE_ROUTER_H_
+#define CHROMECAST_UI_BACK_GESTURE_ROUTER_H_
+
+namespace chromecast {
+
+// Helper class for exposing gesture events to a remote process.
+class BackGestureRouter {
+ public:
+  class Delegate {
+   public:
+    virtual void SetCanGoBack(bool can_go_back) = 0;
+  };
+  virtual void SetBackGestureDelegate(Delegate* delegate) = 0;
+};
+
+}  // namespace chromecast
+
+#endif  // CHROMECAST_UI_BACK_GESTURE_ROUTER_H_