[iOS Clean] Created OverlayService.

ios/clean/chrome/browser/ui/overlays/browser_overlay_queue.h

+// Copyright 2017 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 IOS_CLEAN_CHROME_BROWSER_UI_OVERLAYS_BROWSER_OVERLAY_QUEUE_H_
+#define IOS_CLEAN_CHROME_BROWSER_UI_OVERLAYS_BROWSER_OVERLAY_QUEUE_H_
+
+#import <Foundation/Foundation.h>
+
+#import "ios/clean/chrome/browser/ui/overlays/overlay_queue.h"
+#import "ios/shared/chrome/browser/ui/browser_list/browser_user_data.h"
+
+// Class used to queue overlays to display over the browser content area
+// regardless of which WebState's content is currently visible.
+class BrowserOverlayQueue : public BrowserUserData<BrowserOverlayQueue>,
+                            public OverlayQueue {
+ public:
+  ~BrowserOverlayQueue() override;
+
+  // OverlayQueue:
+  void StartNextOverlay() override;
+  void ReplaceVisibleOverlay(BrowserCoordinator* overlay_coordinator) override;
+  void OverlayWasStopped(BrowserCoordinator* overlay_coordinator) override;
+
+  // Adds |overlay_coordinator| to the queue.  |overlay_parent| will be used as
+  // the parent coordinator when StartNextOverlay() is called.
+  void AddBrowserOverlay(BrowserCoordinator* overlay_coordinator,
+                         BrowserCoordinator* overlay_parent);
+
+ private:
+  friend class BrowserUserData<BrowserOverlayQueue>;
+  // The parent coordinators added with each overlay.
+  NSMutableArray<BrowserCoordinator*>* overlay_parents_;
+
+  // Private constructor.
+  explicit BrowserOverlayQueue(Browser* browser);
+
+  DISALLOW_COPY_AND_ASSIGN(BrowserOverlayQueue);
+};
+
+#endif  // IOS_CLEAN_CHROME_BROWSER_UI_OVERLAYS_BROWSER_OVERLAY_QUEUE_H_