Introduce WebStateList to manage a list of web::WebState.

ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.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_SHARED_CHROME_BROWSER_TABS_WEB_STATE_LIST_OBSERVER_BRIDGE_H_
+#define IOS_SHARED_CHROME_BROWSER_TABS_WEB_STATE_LIST_OBSERVER_BRIDGE_H_
+
+#import <Foundation/Foundation.h>
+
+#include "base/macros.h"
+#import "ios/shared/chrome/browser/tabs/web_state_list_observer.h"
+
+// Protocol that correspond to WebStateListObserver API. Allows registering
+// Objective-C objects to listen to WebStateList events.
+@protocol WebStateListObserving<NSObject>
+
+@optional
+
+// Invoked after a new WebState has been added to the WebStateList at the
+// specified index.
+- (void)webStateList:(WebStateList*)webStateList
+    didInsertWebState:(web::WebState*)webState
+              atIndex:(int)index;
+
+// Invoked after the WebState at the specified index is moved to another index.
+- (void)webStateList:(WebStateList*)webStateList
+     didMoveWebState:(web::WebState*)webState
+           fromIndex:(int)fromIndex
+             toIndex:(int)toIndex;
+
+// Invoked after the WebState at the specified index is replaced by another
+// WebState.
+- (void)webStateList:(WebStateList*)webStateList
+    didReplaceWebState:(web::WebState*)oldWebState
+          withWebState:(web::WebState*)newWebState
+               atIndex:(int)index;
+
+// Invoked after the WebState at the specified index has been detached. The
+// WebState is still valid but is no longer in the WebStateList.
+- (void)webStateList:(WebStateList*)webStateList
+    didDetachWebState:(web::WebState*)webState
+              atIndex:(int)index;
+
+@end
+
+// Observer that bridges WebStateList events to an Objective-C observer that
+// implements the WebStateListObserver protocol (the observer is owned).
+class WebStateListObserverBridge : public WebStateListObserver {
+ public:
+  explicit WebStateListObserverBridge(id<WebStateListObserving> observer);
+  ~WebStateListObserverBridge() override;
+
+ private:
+  // WebStateListObserver implementation.
+  void WebStateInsertedAt(WebStateList* web_state_list,
+                          web::WebState* web_state,
+                          int index) override;
+  void WebStateMoved(WebStateList* web_state_list,
+                     web::WebState* web_state,
+                     int from_index,
+                     int to_index) override;
+  void WebStateReplacedAt(WebStateList* web_state_list,
+                          web::WebState* old_web_state,
+                          web::WebState* new_web_state,
+                          int index) override;
+  void WebStateDetachedAt(WebStateList* web_state_list,
+                          web::WebState* web_state,
+                          int index) override;
+
+  id<WebStateListObserving> observer_;
+
+  DISALLOW_COPY_AND_ASSIGN(WebStateListObserverBridge);
+};
+
+#endif  // IOS_SHARED_CHROME_BROWSER_TABS_WEB_STATE_LIST_OBSERVER_BRIDGE_H_