[ios] Extend WebStateListObserver amd WebStateListDelegate APIs.

ios/chrome/browser/tabs/tab_model_observers_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/chrome/browser/tabs/tab_model_observers_bridge.h"
 
 #include "base/logging.h"
 #import "ios/chrome/browser/tabs/legacy_tab_helper.h"
 #import "ios/chrome/browser/tabs/tab_model.h"
 #import "ios/chrome/browser/tabs/tab_model_observers.h"
@@ skipping 15 matching lines @@
     _tabModel = tabModel;
     _tabModelObservers = tabModelObservers;
   }
   return self;
 }
 
 #pragma mark WebStateListObserving
 
 - (void)webStateList:(WebStateList*)webStateList
     didInsertWebState:(web::WebState*)webState
-              atIndex:(int)index {
-  DCHECK_GE(index, 0);
+              atIndex:(int)atIndex {

[rohitrao (ping after 24h), 2017/03/24 01:20:52]

Why this change?

[sdefresne, 2017/03/24 09:26:18]

Just consistency when naming the parameter (as detailed in the CL description).
I called it |index| in half the methods and |atIndex| in the others. I settled
on |atIndex| because it seemed more common on the old code base, but I can use
|index| if you prefer.

[rohitrao (ping after 24h), 2017/03/24 14:18:09]

I prefer index, but I don't feel strongly.

+  DCHECK_GE(atIndex, 0);
   [_tabModelObservers tabModel:_tabModel
                   didInsertTab:LegacyTabHelper::GetTabForWebState(webState)
-                       atIndex:static_cast<NSUInteger>(index)
+                       atIndex:static_cast<NSUInteger>(atIndex)
                   inForeground:NO];
   [_tabModelObservers tabModelDidChangeTabCount:_tabModel];
 }
 
 - (void)webStateList:(WebStateList*)webStateList
      didMoveWebState:(web::WebState*)webState
            fromIndex:(int)fromIndex
              toIndex:(int)toIndex {
   DCHECK_GE(fromIndex, 0);
   DCHECK_GE(toIndex, 0);
   [_tabModelObservers tabModel:_tabModel
                     didMoveTab:LegacyTabHelper::GetTabForWebState(webState)
                      fromIndex:static_cast<NSUInteger>(fromIndex)
                        toIndex:static_cast<NSUInteger>(toIndex)];
 }
 
 - (void)webStateList:(WebStateList*)webStateList
     didReplaceWebState:(web::WebState*)oldWebState
           withWebState:(web::WebState*)newWebState
-               atIndex:(int)index {
-  DCHECK_GE(index, 0);
+               atIndex:(int)atIndex {
+  DCHECK_GE(atIndex, 0);
   [_tabModelObservers tabModel:_tabModel
                  didReplaceTab:LegacyTabHelper::GetTabForWebState(oldWebState)
                        withTab:LegacyTabHelper::GetTabForWebState(newWebState)
-                       atIndex:static_cast<NSUInteger>(index)];
+                       atIndex:static_cast<NSUInteger>(atIndex)];
 }
 
 - (void)webStateList:(WebStateList*)webStateList
     didDetachWebState:(web::WebState*)webState
-              atIndex:(int)index {
-  DCHECK_GE(index, 0);
+              atIndex:(int)atIndex {
+  DCHECK_GE(atIndex, 0);
   [_tabModelObservers tabModel:_tabModel
                   didRemoveTab:LegacyTabHelper::GetTabForWebState(webState)
-                       atIndex:static_cast<NSUInteger>(index)];
+                       atIndex:static_cast<NSUInteger>(atIndex)];
   [_tabModelObservers tabModelDidChangeTabCount:_tabModel];
 }
 
 - (void)webStateList:(WebStateList*)webStateList
     didChangeActiveWebState:(web::WebState*)newWebState
                 oldWebState:(web::WebState*)oldWebState
                     atIndex:(int)atIndex
                  userAction:(BOOL)userAction {
   if (!newWebState)
     return;
 
   // If there is no new active WebState, then it means that the atIndex will be
   // set to WebStateList::kInvalidIndex, so only check for a positive index if
   // there is a new WebState.
   DCHECK_GE(atIndex, 0);
 
   Tab* oldTab =
       oldWebState ? LegacyTabHelper::GetTabForWebState(oldWebState) : nil;
   [_tabModelObservers tabModel:_tabModel
             didChangeActiveTab:LegacyTabHelper::GetTabForWebState(newWebState)
                    previousTab:oldTab
                        atIndex:static_cast<NSUInteger>(atIndex)];
 }
 
 @end