[iOS Clean] Created OverlayService.

ios/clean/chrome/browser/ui/web_contents/overlays/web_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_WEB_CONTENTS_OVERLAYS_WEB_OVERLAY_COORDINATOR_H_
+#define IOS_CLEAN_CHROME_BROWSER_UI_WEB_CONTENTS_OVERLAYS_WEB_OVERLAY_COORDINATOR_H_
+
+#import <Foundation/Foundation.h>
+
+#import "ios/shared/chrome/browser/ui/coordinators/browser_coordinator.h"
+
+namespace web {
+class WebState;
+}
+
+// An overlay coordinator requested by a WKWebView.  These coordinators own the

[marq (ping after 24h), 2017/06/02 16:14:11]

Nit: WKWebView is an implementation detail inside the web layer. The ui layer
generally deals with WebStates.

[kkhorimoto, 2017/06/03 00:37:32]

I've generalized this and other WebOverlay classes to simply reference Overlays.

+// completion handlers supplied by WebKit and are responsible for cancelling
+// them if necessary.  This interface is meant to be subclassed for JavaScript
+// dialogs, HTTP authentication dialogs, etc.
+@interface WebOverlayCoordinator : BrowserCoordinator
+
+// Designated initializer.  |webState| is the WebState whose WKWebView is
+// requesting the overlay.
+- (instancetype)initWithWebState:(web::WebState*)webState
+    NS_DESIGNATED_INITIALIZER;
+- (instancetype)init NS_UNAVAILABLE;
+
+// Starts this WebOverlayCoordinator over |web_coordinator|.  |web_coordinator|
+// is expected to be displaying the WKWebView that requested the overlay.
+- (void)startOverlayingWebCoordinator:(BrowserCoordinator*)webCoordinator;

[marq (ping after 24h), 2017/06/02 16:14:11]

Wouldn't this just be this coordinator's parent?

[kkhorimoto, 2017/06/03 00:37:32]

When this is called, there is no parent yet.  All the overlay functionality is
private to BrowserCoordinator+Internal, so this is needed as an entry point to
properly set up the overlay state.

+
+// Executes its WebKit completion handler with null parameters. WebKit
+// completion handlers throw exceptions if they are deallocated without
+// being executed.
+- (void)cancelWebKitCompletion;

[marq (ping after 24h), 2017/06/02 16:14:11]

This very much feels like it shouldn't be part of the public API. Coordinators
should avoid exposing implementation details as much as possible.

[kkhorimoto, 2017/06/03 00:37:32]

I've generalized this so that it no longer refers to WebKit completion blocks. 

+
+@end
+
+#endif  // IOS_CLEAN_CHROME_BROWSER_UI_WEB_CONTENTS_OVERLAYS_WEB_OVERLAY_COORDINATOR_H_