Add WebStateListOrderController to control WebState insertion.

ios/shared/chrome/browser/tabs/web_state_list.h

 // 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.
 
 #ifndef IOS_SHARED_CHROME_BROWSER_TABS_WEB_STATE_LIST_H_
 #define IOS_SHARED_CHROME_BROWSER_TABS_WEB_STATE_LIST_H_
 
 #include <memory>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/observer_list.h"
+#include "ui/base/page_transition_types.h"
 
 class WebStateListObserver;
+class WebStateListOrderController;
 
 namespace web {
 class WebState;
 }
 
 // Manages a list of WebStates. May owns the WebState depending on the ownership
 // setting (initialised during construction, should eventually always be "owned"
 // once ownership of Tab is sane, see http://crbug.com/546222 for progress).
 class WebStateList {
  public:
@@ skipping 45 matching lines @@
   int GetIndexOfLastWebStateOpenedBy(const web::WebState* opener,
                                      int start_index,
                                      bool use_group) const;
 
   // Inserts the specified WebState at the specified index with an optional
   // opener (null if there is no opener).
   void InsertWebState(int index,
                       web::WebState* web_state,
                       web::WebState* opener);
 
+  // Inserts the specified WebState at the best position in the WebStateList
+  // given the specified transition, opener (optional, may be null), etc. It
+  // defaults to inserting the WebState at the end of the list.
+  void AppendWebState(ui::PageTransition transition,
+                      web::WebState* web_state,
+                      web::WebState* opener);
+
   // Moves the WebState at the specified index to another index.
   void MoveWebStateAt(int from_index, int to_index);
 
   // Replaces the WebState at the specified index with new WebState. Returns
   // the old WebState at that index to the caller (abandon ownership of the
   // returned WebState). An optional opener for the new WebState may be passed.
   web::WebState* ReplaceWebStateAt(int index,
                                    web::WebState* web_state,
                                    web::WebState* opener);
 
@@ skipping 21 matching lines @@
   // same session.
   int GetIndexOfNthWebStateOpenedBy(const web::WebState* opener,
                                     int start_index,
                                     bool use_group,
                                     int n) const;
 
   class WebStateWrapper;
   const WebStateOwnership web_state_ownership_;
   std::vector<std::unique_ptr<WebStateWrapper>> web_state_wrappers_;
 
+  // An object that determines where new WebState should be inserted and where
+  // selection should move when a WebState is detached.
+  std::unique_ptr<WebStateListOrderController> order_controller_;
+
   // List of observers notified of changes to the model.
   base::ObserverList<WebStateListObserver, true> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(WebStateList);
 };
 
 #endif  // IOS_SHARED_CHROME_BROWSER_TABS_WEB_STATE_LIST_H_