[views] Changes iteration over |children_| to use range-based for loops (reland)

ui/views/view.h

 // Copyright (c) 2012 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 UI_VIEWS_VIEW_H_
 #define UI_VIEWS_VIEW_H_
 
 #include <stddef.h>
 
 #include <algorithm>
@@ skipping 1448 matching lines @@
   int group_;
 
   // Tree operations -----------------------------------------------------------
 
   // This view's parent.
   View* parent_;
 
   // This view's children.
   Views children_;
 
+#if DCHECK_IS_ON()
+  // True while iterating over |children_|. Used to detect and DCHECK when
+  // |children_| is mutated during iteration.
+  mutable bool iterating_;
+#endif
+
   // Size and disposition ------------------------------------------------------
 
   // This View's bounds in the parent coordinate system.
   gfx::Rect bounds_;
 
   // Whether this view is visible.
   bool visible_;
 
   // Whether this view is enabled.
   bool enabled_;
@@ skipping 104 matching lines @@
   // Observers -------------------------------------------------------------
 
   base::ObserverList<ViewObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(View);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_VIEW_H_