[iOS Clean] Created OverlayService.

ios/clean/chrome/browser/ui/overlays/overlay_coordinator.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_WEB_OVERLAY_COORDINATOR_H_
+#define IOS_CLEAN_CHROME_BROWSER_UI_OVERLAYS_WEB_OVERLAY_COORDINATOR_H_
+
+#import <Foundation/Foundation.h>
+
+#import "ios/shared/chrome/browser/ui/coordinators/browser_coordinator.h"
+
+namespace web {
+class WebState;
+}
+
+// OverlayCoordinators are queued on a per-WebState basis using OverlayQueue.
+// OverlayScheduler manages switching the foreground tab so that the next
+// WebState with a queued overlay is visible.
+@interface OverlayCoordinator : BrowserCoordinator
+
+// Designated initializer.  |webState| is used to for OverlaySchedulerCommands.
+- (instancetype)initWithWebState:(web::WebState*)webState
+    NS_DESIGNATED_INITIALIZER;
+- (instancetype)init NS_UNAVAILABLE;
+
+// The WebState presenting this overlay.
+@property(nonatomic, readonly) web::WebState* webState;
+
+// Starts this overlay over |coordinator|'s UI.  |coordinator| is expected to be
+// displaying the content view of the overlay's corresponding WebState.
+- (void)startOverlayingCoordinator:(BrowserCoordinator*)coordinator;
+
+// Performs cleanup tasks for the overlay. If a WebState is destroyed before its
+// queued overlays are presented, the overlays are removed from the queue.
+// Rather than relying on |-dealloc| to perform cleanup, |-cancelOverlay| can be
+// used to perform cleanup tasks deterministically.
+- (void)cancelOverlay;

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

How is this different from -stop?

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

It's possible for these coordinators to be cancelled without their UI ever being
started (e.g. if a background Tab enqueues a dialog, but is closed before the
dialog can  be displayed).

+
+@end
+
+#endif  // IOS_CLEAN_CHROME_BROWSER_UI_OVERLAYS_WEB_OVERLAY_COORDINATOR_H_