[iOS Clean] Created OverlayService.

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

Index: ios/clean/chrome/browser/ui/overlays/browser_overlay_queue.mm
diff --git a/ios/clean/chrome/browser/ui/overlays/browser_overlay_queue.mm b/ios/clean/chrome/browser/ui/overlays/browser_overlay_queue.mm
new file mode 100644
index 0000000000000000000000000000000000000000..76e93547920a2d84c466278bd89bc7f6b93bcef1
--- /dev/null
+++ b/ios/clean/chrome/browser/ui/overlays/browser_overlay_queue.mm
@@ -0,0 +1,52 @@
+// 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/browser_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_BROWSER_USER_DATA_KEY(BrowserOverlayQueue);
+
+BrowserOverlayQueue::BrowserOverlayQueue(Browser* browser)
+    : overlay_parents_([[NSMutableArray alloc] init]) {}
+
+BrowserOverlayQueue::~BrowserOverlayQueue() {}
+
+void BrowserOverlayQueue::StartNextOverlay() {
+  DCHECK(HasQueuedOverlays());
+  DCHECK_EQ(GetCount(), [overlay_parents_ count]);
+  DCHECK(!IsShowingOverlay());
+  [GetFirstOverlay() startOverlayingCoordinator:[overlay_parents_ firstObject]];
+  OverlayWasStarted();
+}
+
+void BrowserOverlayQueue::ReplaceVisibleOverlay(
+    BrowserCoordinator* overlay_coordinator) {
+  DCHECK(IsShowingOverlay());
+  // Prepend the current overlay's parent to |overlay_parents_| so that the
+  // replacement overlay can also use that as its parents.
+  [overlay_parents_ addObject:[overlay_parents_ firstObject]];
+  OverlayQueue::ReplaceVisibleOverlay(overlay_coordinator);
+}
+
+void BrowserOverlayQueue::OverlayWasStopped(
+    BrowserCoordinator* overlay_coordinator) {
+  DCHECK_EQ(GetFirstOverlay(), overlay_coordinator);
+  [overlay_parents_ removeObjectAtIndex:0];
+  OverlayQueue::OverlayWasStopped(overlay_coordinator);
+}
+
+void BrowserOverlayQueue::AddBrowserOverlay(
+    BrowserCoordinator* overlay_coordinator,
+    BrowserCoordinator* overlay_parent) {
+  DCHECK(overlay_coordinator);
+  DCHECK(overlay_parent);
+  [overlay_parents_ addObject:overlay_parent];
+  OverlayQueue::AddOverlay(overlay_coordinator);
+}