[iOS Clean] Created OverlayService.

ios/clean/chrome/browser/ui/overlays/overlay_service.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_OVERLAYS_OVERLAY_SERVICE_H_
+#define IOS_CLEAN_CHROME_BROWSER_UI_OVERLAYS_OVERLAY_SERVICE_H_
+
+#include "base/macros.h"
+#include "components/keyed_service/core/keyed_service.h"
+
+namespace web {
+class WebState;
+}
+
+class Browser;
+@class BrowserCoordinator;
+
+// OverlayService allows for the easy presentation and dismissal of overlay

[marq (ping after 24h), 2017/06/21 09:41:54]

The division of responsibilities between the OverlayService and the
OverlayScheduler isn't clear to me. 

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

The main entry point to this overlay system is adding overlays to an
OverlayQueue.  I thought that it wasn't as clear, so defining a single service
interface helps expose a more understandable API for overlaying.  Also, since
this exists at a ChromeBrowserState-level, it can handle adding/removing
observers for browsers, and is easily accessible from any BrowserCoordinator. 
I've moved the implementation files into an internal/ directory to make it
clearer that clients of this system should include the service-level target.

[marq (ping after 24h), 2017/06/23 10:42:01]

I don't agree that adding this service makes the necessary interactions clearer.
For example, I think it's fine for the web container coordinator to grab the
webstate overlay queue directly.

Also, remember that we don't want to assume a 1:1 correspondence between
BrowserState and browsers -- in the future we may have multiple browsers for the
same BrowserState.

I also don't like that we need to add six files (factory, service, service_impl,
.h and .mm) to do this.

+// cordinators.  Overlays are modal and displayed in the order in which this
+// service receives them.  If an overlay is added to this service while one is
+// already presented, it will be queued until that current overlay is stopped.
+class OverlayService : public KeyedService {
+ public:
+  OverlayService() = default;
+  ~OverlayService() override = default;
+
+  // Whether an overlay is currently displayed for |browser|.  This will return
+  // true for both WebState-specific or Browser-level overlays.
+  virtual bool IsBrowserShowingOverlay(Browser* browser) const = 0;
+
+  // Replaces |browser|'s currently-visible overlay with |overlay_coordinator|.
+  // The replacement overlay will use the visible overlays parent as its own.
+  // This will replace the current overlay regardless of if it's WebState-
+  // specific.
+  virtual void ReplaceVisibleOverlay(BrowserCoordinator* overlay_coordinator,
+                                     Browser* browser) = 0;
+
+  // Cancels all scheduled overlays added to this service.  If an overlay is
+  // currently visible, it will be stopped.
+  virtual void CancelOverlays() = 0;
+
+  // Browser-specific overlays:
+
+  // Shows |overlay_coordinator| over |parent_coordinator|'s UI.
+  virtual void ShowOverlayForBrowser(BrowserCoordinator* overlay_coordinator,
+                                     BrowserCoordinator* parent_coordiantor,
+                                     Browser* browser) = 0;
+
+  // WebState-specific overlays:
+
+  // Switches the active WebState to |web_state| and displays
+  // |overlay_coordinator|'s UI over it.
+  virtual void ShowOverlayForWebState(BrowserCoordinator* overlay_coordinator,
+                                      web::WebState* web_state) = 0;
+
+  // Cancels all scheduled overlays for |web_state|.  If a |web_state|-specific
+  // overlay is currently visible, it will be stopped.
+  virtual void CancelOverlayForWebState(web::WebState* web_state) = 0;
+
+  // Overlays added via ShowOverlayForWebState() can only be started when their
+  // associated WebState's content are is visible.  When a coordinator showing
+  // a WebState's content is started, it can notify the OverlayService to use
+  // itself as the parent for that WebState's overlays.
+  virtual void SetWebStateParentCoordinator(
+      BrowserCoordinator* parent_coordinator,
+      web::WebState* web_state) = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(OverlayService);
+};
+
+#endif  // IOS_CLEAN_CHROME_BROWSER_UI_OVERLAYS_OVERLAY_SERVICE_H_