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

ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.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/shared/chrome/browser/tabs/web_state_list_observer_bridge.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+WebStateListObserverBridge::WebStateListObserverBridge(
+    id<WebStateListObserver> observer)
+    : observer_(observer) {}
+
+WebStateListObserverBridge::~WebStateListObserverBridge() {}
+
+void WebStateListObserverBridge::WebStateInsertedAt(
+    WebStateList* web_state_list,
+    web::WebState* web_state,
+    size_t index) {
+  SEL selector = @selector(webStateList:webStateInserted:atIndex:);
+  if (![observer_ respondsToSelector:selector])
+    return;
+
+  [observer_ webStateList:web_state_list
+         webStateInserted:web_state
+                  atIndex:index];
+}
+
+void WebStateListObserverBridge::WebStateMoved(WebStateList* web_state_list,
+                                               web::WebState* web_state,
+                                               size_t from_index,
+                                               size_t to_index) {
+  SEL selector = @selector(webStateList:webStateMoved:fromIndex:toIndex:);
+  if (![observer_ respondsToSelector:selector])
+    return;
+
+  [observer_ webStateList:web_state_list
+            webStateMoved:web_state
+                fromIndex:from_index
+                  toIndex:to_index];
+}
+
+void WebStateListObserverBridge::WebStateReplacedAt(
+    WebStateList* web_state_list,
+    web::WebState* old_web_state,
+    web::WebState* new_web_state,
+    size_t index) {
+  SEL selector = @selector(webStateList:webStateReplaced:byWebState:atIndex:);
+  if (![observer_ respondsToSelector:selector])
+    return;
+
+  [observer_ webStateList:web_state_list
+         webStateReplaced:old_web_state
+               byWebState:new_web_state
+                  atIndex:index];
+}
+
+void WebStateListObserverBridge::WebStateRemovedAt(WebStateList* web_state_list,
+                                                   web::WebState* web_state,
+                                                   size_t index) {
+  SEL selector = @selector(webStateList:webStateRemoved:atIndex:);
+  if (![observer_ respondsToSelector:selector])
+    return;
+
+  [observer_ webStateList:web_state_list
+          webStateRemoved:web_state
+                  atIndex:index];
+}