[iOS Clean] Created OverlayService.

ios/clean/chrome/browser/ui/overlays/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_OVERLAYS_OVERLAY_SCHEDULER_H_
+#define IOS_CLEAN_CHROME_BROWSER_UI_OVERLAYS_OVERLAY_SCHEDULER_H_
+
+#include <Foundation/Foundation.h>
+
+#import "ios/clean/chrome/browser/ui/commands/overlay_commands.h"
+
+@protocol TabGridCommands;
+class WebStateList;
+
+// An object that manages displaying a WebState's content view before starting

[marq (ping after 24h), 2017/06/14 10:02:32]

Document clearly how this class may trigger webstates to be activated.

[kkhorimoto, 2017/06/15 08:26:28]

Done.

+// an overlay from its OverlayQueue.
+@interface OverlayScheduler : NSObject<OverlaySchedulerCommands>

[marq (ping after 24h), 2017/06/14 10:02:32]

Unit tests for this class?

[kkhorimoto, 2017/06/15 08:26:28]

Ack.  Will be in next patch.

+
+// Designated initializer for a OverlayScheduler that uses |dispatcher| to
+// switch the foreground tab and present overlays.
+- (instancetype)initWithWebStateList:(WebStateList*)webStateList
+                          dispatcher:
+                              (id<TabGridCommands, OverlayPresentationCommands>)
+                                  dispatcher NS_DESIGNATED_INITIALIZER;
+- (instancetype)init NS_UNAVAILABLE;
+
+@end
+
+#endif  // IOS_CLEAN_CHROME_BROWSER_UI_OVERLAYS_OVERLAY_SCHEDULER_H_