Add View::AddedToWidget and RemovedFromWidget.

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 1098 matching lines @@
   virtual void VisibilityChanged(View* starting_from, bool is_visible);
 
   // This method is invoked when the parent NativeView of the widget that the
   // view is attached to has changed and the view hierarchy has not changed.
   // ViewHierarchyChanged() is called when the parent NativeView of the widget
   // that the view is attached to is changed as a result of changing the view
   // hierarchy. Overriding this method is useful for tracking which
   // FocusManager manages this view.
   virtual void NativeViewHierarchyChanged();
 
+  // This method is invoked for a view when it is attached to a hierarchy with
+  // a widget, i.e. GetWidget() starts returning a non-null result.
+  virtual void AddedToWidget();
+
+  // This method is invoked for a view when it is removed from a hierarchy with
+  // a widget.
+  virtual void RemovedFromWidget();
+
   // Painting ------------------------------------------------------------------
 
   // Responsible for calling Paint() on child Views. Override to control the
   // order child Views are painted.
   virtual void PaintChildren(const ui::PaintContext& context);
 
   // Override to provide rendering in any part of the View's bounds. Typically
   // this is the "contents" of the view. If you override this method you will
   // have to call the subsequent OnPaint*() methods manually.
   virtual void OnPaint(gfx::Canvas* canvas);
@@ skipping 172 matching lines @@
   void PropagateRemoveNotifications(View* old_parent, View* new_parent);
 
   // Call ViewHierarchyChanged() for all children.
   void PropagateAddNotifications(const ViewHierarchyChangedDetails& details);
 
   // Propagates NativeViewHierarchyChanged() notification through all the
   // children.
   void PropagateNativeViewHierarchyChanged();
 
   // Takes care of registering/unregistering accelerators if
-  // |register_accelerators| true and calls ViewHierarchyChanged().
+  // |register_accelerators| true, calls ViewHierarchyChanged() and
+  // AddedToWidget() or RemovedFromWidget() if necessary.
   void ViewHierarchyChangedImpl(bool register_accelerators,
                                 const ViewHierarchyChangedDetails& details);
 
   // Invokes OnNativeThemeChanged() on this and all descendants.
   void PropagateNativeThemeChanged(const ui::NativeTheme* theme);
 
   // Size and disposition ------------------------------------------------------
 
   // Call VisibilityChanged() recursively for all children.
   void PropagateVisibilityNotifications(View* from, bool is_visible);
@@ skipping 162 matching lines @@
   int group_;
 
   // Tree operations -----------------------------------------------------------
 
   // This view's parent.
   View* parent_;
 
   // This view's children.
   Views children_;
 
+  // The widget this view is (possibily indirectly) attached to.
+  Widget* attached_widget_;

[sky, 2017/02/24 18:26:14]

We shouldn't need to cache the widget. This likely requires changing the
signature of ViewHierarchyChangedImpl() to indicate one of added to widget,
removed from widget or no change in widget status.

[msimonides, 2017/02/27 09:52:28]

Done.

+
 #if DCHECK_IS_ON()
   // True while iterating over |children_|. Used to detect and DCHECK when
   // |children_| is mutated during iteration.
   mutable bool iterating_;
 #endif
 
   bool can_process_events_within_subtree_;
 
   // Size and disposition ------------------------------------------------------
 
@@ skipping 119 matching lines @@
   // Observers -------------------------------------------------------------
 
   base::ObserverList<ViewObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(View);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_VIEW_H_