[iOS Clean] Created OverlayService.

ios/clean/chrome/browser/ui/overlays/overlay_queue_observer.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_queue_observer.h"

[marq (ping after 24h), 2017/06/21 09:41:53]

I think you can just put the defaults and empty blocks into the header; there's
no need for an .mm file (compare to web_state_observer.h).

[kkhorimoto, 2017/06/23 06:11:16]

Done.

+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+OverlayQueueObserver::OverlayQueueObserver() = default;
+
+OverlayQueueObserver::~OverlayQueueObserver() = default;
+
+void OverlayQueueObserver::OverlayQueueDidAddOverlay(OverlayQueue* queue) {}
+
+void OverlayQueueObserver::OverlayQueueWillReplaceVisibleOverlay(
+    OverlayQueue* queue) {}
+
+void OverlayQueueObserver::OverlayQueueDidStopVisibleOverlay(
+    OverlayQueue* queue) {}
+
+void OverlayQueueObserver::OverlayQueueDidCancelOverlays(OverlayQueue* queue) {}