WebStateList is an array of web::WebState* wrappers.

ios/chrome/browser/tabs/web_state_list.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/chrome/browser/tabs/web_state_list.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+@implementation WebStateList {
+  NSMutableArray<id<WebStateHandle>>* _list;
+}
+
+#pragma mark - Lifecycle
+
+- (instancetype)init {
+  if ((self = [super init])) {
+    _list = [[NSMutableArray alloc] init];
+  }
+  return self;
+}
+
+#pragma mark - NSFastEnumeration
+
+- (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState*)state
+                                  objects:(id __unsafe_unretained*)buffer
+                                    count:(NSUInteger)len {
+  return [_list countByEnumeratingWithState:state objects:buffer count:len];
+}
+
+#pragma mark - Properties
+
+- (NSUInteger)count {
+  return [_list count];

[marq (ping after 24h), 2017/01/19 13:37:46]

nit: _list.count

[sdefresne, 2017/01/20 14:42:09]

Done.

+}
+
+- (id<WebStateHandle>)firstWebState {
+  return [_list firstObject];

[marq (ping after 24h), 2017/01/19 13:37:46]

nit: _list.firstObject

[sdefresne, 2017/01/20 14:42:09]

Done.

+}
+
+#pragma mark - Public methods, mutation
+
+- (void)addWebState:(id<WebStateHandle>)webState {
+  [_list addObject:webState];
+}
+
+- (void)insertWebState:(id<WebStateHandle>)webState atIndex:(NSUInteger)index {
+  [_list insertObject:webState atIndex:index];
+}
+
+- (void)replaceWebStateAtIndex:(NSUInteger)index
+                  withWebState:(id<WebStateHandle>)webState {
+  [_list replaceObjectAtIndex:index withObject:webState];
+}
+
+- (void)removeWebState:(id<WebStateHandle>)webState {
+  [_list removeObject:webState];
+}
+
+#pragma mark - Public methods, queries
+
+- (BOOL)containsWebState:(id<WebStateHandle>)webSate {
+  return [_list containsObject:webSate];
+}
+
+- (id<WebStateHandle>)webStateAtIndex:(NSUInteger)index {

[marq (ping after 24h), 2017/01/19 14:35:11]

Do we want to guard against range exceptions by returning nil if index >=
self.count?

[sdefresne, 2017/01/20 14:42:09]

I've added a DCHECK, WDYT?

[marq (ping after 24h), 2017/01/20 14:49:17]

Doesn't that just trade one exception for another? If you think it's better to
throw for a range exception then that's fine, but I was thinking we could return
nil in that case instead of throwing.

+  return [_list objectAtIndex:index];
+}
+
+- (NSUInteger)indexOfWebState:(id<WebStateHandle>)webState {
+  return [_list indexOfObject:webState];
+}
+
+#pragma mark - Public methods, deprecated
+
+- (NSArray*)allWebStates {
+  return [_list copy];
+}
+
+@end