[iOS Clean] Created OverlayService.

ios/clean/chrome/browser/ui/overlays/overlay_coordinator.mm

+// 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.
+
+#import "ios/clean/chrome/browser/ui/overlays/overlay_coordinator.h"
+
+#import "base/logging.h"
+#import "ios/clean/chrome/browser/ui/commands/overlay_commands.h"
+#import "ios/clean/chrome/browser/ui/overlays/overlay_queue.h"
+#import "ios/shared/chrome/browser/ui/browser_list/browser.h"
+#import "ios/shared/chrome/browser/ui/commands/command_dispatcher.h"
+#import "ios/shared/chrome/browser/ui/coordinators/browser_coordinator+internal.h"
+#import "ios/web/public/web_state/web_state.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+@implementation OverlayCoordinator
+@synthesize webState = _webState;
+
+- (instancetype)initWithWebState:(web::WebState*)webState {
+  DCHECK(webState);
+  if ((self = [super init])) {
+    _webState = webState;
+  }
+  return self;
+}
+
+#pragma mark - Public
+
+- (void)startOverlayingCoordinator:(BrowserCoordinator*)coordinator {
+  DCHECK([coordinator canAddOverlayCoordinator:self]);
+  [coordinator addOverlayCoordinator:self];

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

I think we don't need both the overlay mechanism inside BrowserCoordinator *and*
the queuing/scheduling stuff you have here. I like your approach better, and
removing the overlay support from BC means we can treat overlays as children,
regularizing this interface.

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

Acknowledged.  This patch still uses the existing overlay system, but it will be
rebased onto another CL that moves the BrowserCoordinator+Internal overlay
support code to OverlayCoordinator.

+  [self start];
+}
+
+- (void)cancelOverlay {
+  // Implemented by subclasses.

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

The header needs to express that this class is intended to be subclassed.

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

Done.

+}
+
+#pragma mark - BrowserCoordinator
+
+- (void)stop {
+  [super stop];
+  // Stop receiving commands.
+  [self.browser->dispatcher() stopDispatchingToTarget:self];
+  // Remove as the overlay for its parent.
+  [self.parentCoordinator removeOverlayCoordinator];
+  // Notify the WebOverlayQueue that this coordinator has stopped so that it can
+  // be dequeued.
+  OverlayQueue::FromWebState(self.webState)->OverlayWasStopped(self);
+}
+
+@end