[iOS] Add OverlayPresenter functionality.

This CL adds functionality to OverlayPresenter to drive the
presentation of overlay UI.

It also updates the presenter to observe its WebStateList
and OverlayRequestQueueImpls for the lifetime of the object,
rather than only when a UI delegate is provided.
ShowNextOverlay() no-ops without a UI delegate, and is already
called in scenarios where an overlay may not be shown.

Bug: 941745
Change-Id: Ib8fe7b49bfba3d8624c5acf40f7e0f512d6cd0ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1586776
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Mike Dougherty <michaeldo@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656401}

ios/chrome/browser/overlays/BUILD.gn

@@ -43,6 +43,7 @@ source_set("unit_tests") {
   testonly = true
   sources = [
     "overlay_manager_impl_unittest.mm",
+    "overlay_presenter_unittest.mm",
     "overlay_request_impl_unittest.cc",
     "overlay_request_queue_impl_unittest.mm",
     "overlay_request_unittest.cc",

ios/chrome/browser/overlays/overlay_presenter.h

@@ -5,17 +5,19 @@
 #ifndef IOS_CHROME_BROWSER_OVERLAYS_OVERLAY_PRESENTER_H_
 #define IOS_CHROME_BROWSER_OVERLAYS_OVERLAY_PRESENTER_H_
 
+#include "base/memory/weak_ptr.h"
 #import "ios/chrome/browser/overlays/overlay_request_queue_impl_observer.h"
 #import "ios/chrome/browser/overlays/public/overlay_modality.h"
+#import "ios/chrome/browser/overlays/public/overlay_ui_delegate.h"
 #import "ios/chrome/browser/web_state_list/web_state_list_observer.h"
 
 class OverlayUIDelegate;
 
 // OverlayPresenter is responsible for triggering the presentation of overlay UI
-// at a given modality.  It observes OverlayRequestQueue modifications for the
-// active WebState and triggers the presentation for added requests using the UI
-// delegate.  Additionally, the presenter will manage hiding and showing
-// overlays when the foreground tab is updated.
+// at a given modality.  The presenter:
+// - observes OverlayRequestQueue modifications for the active WebState and
+//   triggers the presentation for added requests using the UI delegate.
+// - manages hiding and showing overlays for active WebState changes.
 class OverlayPresenter : public OverlayRequestQueueImplObserver,
                          public WebStateListObserver {
  public:
@@ -31,13 +33,39 @@ class OverlayPresenter : public OverlayRequestQueueImplObserver,
   void Disconnect();
 
  private:
+  // Setter for the active WebState.  Setting to a new value will hide any
+  // presented overlays and show the next overlay for the new active WebState.
+  void SetActiveWebState(web::WebState* web_state,
+                         WebStateListObserver::ChangeReason reason);
+
   // Fetches the request queue for |web_state|, creating it if necessary.
-  OverlayRequestQueueImpl* GetQueueForWebState(web::WebState* web_state);
+  OverlayRequestQueueImpl* GetQueueForWebState(web::WebState* web_state) const;
+
+  // Returns the request queue for the active WebState.
+  OverlayRequestQueueImpl* GetActiveQueue() const;
+
+  // Returns the front request for the active queue.
+  OverlayRequest* GetActiveRequest() const;
+
+  // Triggers the presentation of the overlay UI for the active request.  Does
+  // nothing if there is no active request or if there is no UI delegate.  Must
+  // only be called when |presenting_| is false.
+  void PresentOverlayForActiveRequest();
+
+  // Notifies this object that |ui_delegate| has finished dismissing the
+  // overlay UI corresponding with |request| in |queue| for |reason|.  This
+  // function is called when the OverlayDismissalCallback provided to the UI
+  // delegate is excuted.
+  void OverlayWasDismissed(OverlayUIDelegate* ui_delegate,
+                           OverlayRequest* request,
+                           OverlayRequestQueueImpl* queue,
+                           OverlayDismissalReason reason);
+
+  // Cancels all overlays for |web_state|.
+  void CancelOverlayUIForWebState(web::WebState* web_state);
 
-  // Starts and stops observing |web_state_list_| and its WebStates request
-  // queues.
-  void StartObserving();
-  void StopObserving();
+  // Cancels all overlays for the Browser.
+  void CancelAllOverlayUI();
 
   // OverlayRequestQueueImplObserver:
   void OnRequestAdded(OverlayRequestQueueImpl* queue,
@@ -63,7 +91,11 @@ class OverlayPresenter : public OverlayRequestQueueImplObserver,
 
   OverlayModality modality_;
   WebStateList* web_state_list_ = nullptr;
+  web::WebState* active_web_state_ = nullptr;
   OverlayUIDelegate* ui_delegate_ = nullptr;
+  bool presenting_ = false;
+  bool detaching_active_web_state_ = false;
+  base::WeakPtrFactory<OverlayPresenter> weak_factory_;
 };
 
 #endif  // IOS_CHROME_BROWSER_OVERLAYS_OVERLAY_PRESENTER_H_