[iOS Clean] Created OverlayService.

ios/clean/chrome/browser/ui/overlay_service/internal/web_state_overlay_queue.mm

Index: ios/clean/chrome/browser/ui/overlay_service/internal/web_state_overlay_queue.mm
diff --git a/ios/clean/chrome/browser/ui/overlay_service/internal/web_state_overlay_queue.mm b/ios/clean/chrome/browser/ui/overlay_service/internal/web_state_overlay_queue.mm
new file mode 100644
index 0000000000000000000000000000000000000000..cb53b65e063a52ee5245996ed718e52e4d9aec12
--- /dev/null
+++ b/ios/clean/chrome/browser/ui/overlay_service/internal/web_state_overlay_queue.mm
@@ -0,0 +1,41 @@
+// 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/overlay_service/internal/web_state_overlay_queue.h"
+
+#include "base/logging.h"
+#import "ios/shared/chrome/browser/ui/coordinators/browser_coordinator.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+DEFINE_WEB_STATE_USER_DATA_KEY(WebStateOverlayQueue);
+
+WebStateOverlayQueue::WebStateOverlayQueue(web::WebState* web_state)
+    : web_state_(web_state), parent_coordinator_(nil) {
+  DCHECK(web_state);
+}
+
+web::WebState* WebStateOverlayQueue::GetWebState() const {
+  return web_state_;
+}
+
+void WebStateOverlayQueue::StartNextOverlay() {
+  DCHECK(parent_coordinator_);
+  DCHECK(HasQueuedOverlays());
+  DCHECK(!IsShowingOverlay());
+  [GetFirstOverlay() startOverlayingCoordinator:parent_coordinator_];
+  OverlayWasStarted();
+}
+
+void WebStateOverlayQueue::AddWebStateOverlay(
+    BrowserCoordinator* overlay_coordinator) {
+  AddOverlay(overlay_coordinator);
+}
+
+void WebStateOverlayQueue::SetWebStateParentCoordinator(
+    BrowserCoordinator* parent_coordinator) {
+  parent_coordinator_ = parent_coordinator;
+}