[iOS Clean] Created OverlayService.

ios/clean/chrome/browser/ui/web_contents/overlays/web_overlay_scheduler.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_WEB_CONTENTS_OVERLAYS_WEB_OVERLAY_SCHEDULER_H_
+#define IOS_CLEAN_CHROME_BROWSER_UI_WEB_CONTENTS_OVERLAYS_WEB_OVERLAY_SCHEDULER_H_
+
+#include <Foundation/Foundation.h>
+
+#import "ios/clean/chrome/browser/ui/commands/web_overlay_commands.h"
+
+@protocol TabGridCommands;
+
+// An object that manages displaying a WebState's content view before starting
+// an overlay from its WebOverlayQueue.
+@interface WebOverlayScheduler : NSObject<WebOverlaySchedulerCommands>
+
+// Designated initializer for a WebOverlayScheduler that uses |dispatcher| to
+// switch the foreground tab and present overlays.
+- (instancetype)initWithDispatcher:
+    (id<TabGridCommands, WebOverlayPresentationCommands>)dispatcher
+    NS_DESIGNATED_INITIALIZER;
+- (instancetype)init NS_UNAVAILABLE;
+
+@end
+
+#endif  // IOS_CLEAN_CHROME_BROWSER_UI_WEB_CONTENTS_OVERLAYS_WEB_OVERLAY_SCHEDULER_H_