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

ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.mm

Index: ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.mm
diff --git a/ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.mm b/ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.mm
new file mode 100644
index 0000000000000000000000000000000000000000..f2d5f720f35172a44705ebbf162422c416f3e1ad
--- /dev/null
+++ b/ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.mm
@@ -0,0 +1,72 @@
+// 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<WebStateListObserving> observer)
+    : observer_(observer) {}
+
+WebStateListObserverBridge::~WebStateListObserverBridge() {}
+
+void WebStateListObserverBridge::WebStateInsertedAt(
+    WebStateList* web_state_list,
+    web::WebState* web_state,
+    int index) {
+  const SEL selector = @selector(webStateList:didInsertWebState:atIndex:);
+  if (![observer_ respondsToSelector:selector])
+    return;
+
+  [observer_ webStateList:web_state_list
+        didInsertWebState:web_state
+                  atIndex:index];
+}
+
+void WebStateListObserverBridge::WebStateMoved(WebStateList* web_state_list,
+                                               web::WebState* web_state,
+                                               int from_index,
+                                               int to_index) {
+  const SEL selector =
+      @selector(webStateList:didMoveWebState:fromIndex:toIndex:);
+  if (![observer_ respondsToSelector:selector])
+    return;
+
+  [observer_ webStateList:web_state_list
+          didMoveWebState: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,
+    int index) {
+  const SEL selector =
+      @selector(webStateList:didReplaceWebState:withWebState:atIndex:);
+  if (![observer_ respondsToSelector:selector])
+    return;
+
+  [observer_ webStateList:web_state_list
+       didReplaceWebState:old_web_state
+             withWebState:new_web_state
+                  atIndex:index];
+}
+
+void WebStateListObserverBridge::WebStateDetachedAt(
+    WebStateList* web_state_list,
+    web::WebState* web_state,
+    int index) {
+  const SEL selector = @selector(webStateList:didDetachWebState:atIndex:);
+  if (![observer_ respondsToSelector:selector])
+    return;
+
+  [observer_ webStateList:web_state_list
+        didDetachWebState:web_state
+                  atIndex:index];
+}