[ios] Extend WebStateListObserver amd WebStateListDelegate APIs.

ios/shared/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/shared/chrome/browser/tabs/web_state_list.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/logging.h"
@@ skipping 196 matching lines @@
   delegate_->WillAddWebState(web_state);
 
   ClearOpenersReferencing(index);
 
   auto& web_state_wrapper = web_state_wrappers_[index];
   web::WebState* old_web_state = web_state_wrapper->ReplaceWebState(web_state);
 
   for (auto& observer : observers_)
     observer.WebStateReplacedAt(this, old_web_state, web_state, index);
 
+  delegate_->WebStateDetached(old_web_state);
   return old_web_state;
 }
 
 web::WebState* WebStateList::DetachWebStateAt(int index) {
   DCHECK(ContainsIndex(index));
   int new_active_index = order_controller_->DetermineNewActiveIndex(index);
 
   web::WebState* old_web_state = web_state_wrappers_[index]->web_state();
+  for (auto& observer : observers_)
+    observer.WillDetachWebStateAt(this, old_web_state, index);
 
   ClearOpenersReferencing(index);
   web_state_wrappers_.erase(web_state_wrappers_.begin() + index);
 
   // Update the active index to prevent observer from seeing an invalid WebState
   // as the active one but only send the WebStateActivatedAt notification after
   // the WebStateDetachedAt one.
   bool active_web_state_was_closed = (index == active_index_);
   if (active_index_ > index)
     --active_index_;
   else if (active_index_ == index)
     active_index_ = new_active_index;
 
   for (auto& observer : observers_)
     observer.WebStateDetachedAt(this, old_web_state, index);
 
   if (active_web_state_was_closed)
     NotifyIfActiveWebStateChanged(old_web_state, false);
 
+  delegate_->WebStateDetached(old_web_state);
   return old_web_state;
 }
 
 void WebStateList::ActivateWebStateAt(int index) {
   DCHECK(ContainsIndex(index));
   web::WebState* old_web_state = GetActiveWebState();
   active_index_ = index;
   NotifyIfActiveWebStateChanged(old_web_state, true);
 }
 
@@ skipping 46 matching lines @@
     } else if (found_index != kInvalidIndex) {
       return found_index;
     }
   }
 
   return found_index;
 }
 
 // static
 const int WebStateList::kInvalidIndex;