Add WebStateListOrderController to control WebState insertion.

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

Index: ios/shared/chrome/browser/tabs/web_state_list.h
diff --git a/ios/shared/chrome/browser/tabs/web_state_list.h b/ios/shared/chrome/browser/tabs/web_state_list.h
index 6d537a7624b44c9adf5e054d708de0a8c61b4100..3190fa19893ae0b6e04373a11c931194ba154d82 100644
--- a/ios/shared/chrome/browser/tabs/web_state_list.h
+++ b/ios/shared/chrome/browser/tabs/web_state_list.h
@@ -10,8 +10,10 @@
 
 #include "base/macros.h"
 #include "base/observer_list.h"
+#include "ui/base/page_transition_types.h"
 
 class WebStateListObserver;
+class WebStateListOrderController;
 
 namespace web {
 class WebState;
@@ -73,6 +75,15 @@ class WebStateList {
                       web::WebState* web_state,
                       web::WebState* opener);
 
+  // Adds a WebState at the best position in the WebStateList given the
+  // specified insertion index, transition, etc. An optional opener for the new
+  // WebState may be passed. Pass kInvalidIndex for |index| to append it to the

[marq (ping after 24h), 2017/02/17 13:33:00]

I would have a mild preference for a separate AppendWebState method instead of
attaching magical behavior to specific input values.

[sdefresne, 2017/02/20 16:12:55]

Done.

+  // WebStateList.
+  void AddWebState(int index,
+                   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);
 
@@ -117,6 +128,10 @@ class WebStateList {
   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_;