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 1083 matching lines @@
   // When a view is removed, it is invoked for all children and grand
   // children. For each of these views, a notification is sent to the
   // view and all parents.
   //
   // When a view is added, a notification is sent to the view, all its
   // parents, and all its children (and grand children)
   //
   // Default implementation does nothing. Override to perform operations
   // required when a view is added or removed from a view hierarchy
   //
   // Refer to comments in struct |ViewHierarchyChangedDetails| for |details|.

[sky, 2017/03/01 20:26:51]

Add a comment here to see AddedToWidget/RemovedFromWidget for detecting when
added/removed from widget.

[msimonides, 2017/03/02 07:48:56]

Done.

   virtual void ViewHierarchyChanged(const ViewHierarchyChangedDetails& details);
 
   // When SetVisible() changes the visibility of a view, this method is
   // invoked for that view as well as all the children recursively.
   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.

[sky, 2017/03/01 20:26:51]

Clarify this is also invoked if a view is moved to a different widget.

[msimonides, 2017/03/02 07:48:56]

Done.

+  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 162 matching lines @@
   void DoRemoveChildView(View* view,
                          bool update_focus_cycle,
                          bool update_tool_tip,
                          bool delete_removed_view,
                          View* new_parent);
 
   // Call ViewHierarchyChanged() for all child views and all parents.
   // |old_parent| is the original parent of the View that was removed.
   // If |new_parent| is not NULL, the View that was removed will be reparented
   // to |new_parent| after the remove operation.
-  void PropagateRemoveNotifications(View* old_parent, View* new_parent);
+  // If is_removed_from_widget is true, calls RemovedFromWidget for all
+  // children.
+  void PropagateRemoveNotifications(View* old_parent,
+                                    View* new_parent,
+                                    bool is_removed_from_widget);
 
   // Call ViewHierarchyChanged() for all children.
-  void PropagateAddNotifications(const ViewHierarchyChangedDetails& details);
+  // If is_added_to_widget is true, calls AddedToWidget for all children.
+  void PropagateAddNotifications(const ViewHierarchyChangedDetails& details,
+                                 bool is_added_to_widget);
 
   // Propagates NativeViewHierarchyChanged() notification through all the
   // children.
   void PropagateNativeViewHierarchyChanged();
 
   // Takes care of registering/unregistering accelerators if
   // |register_accelerators| true and calls ViewHierarchyChanged().
   void ViewHierarchyChangedImpl(bool register_accelerators,
                                 const ViewHierarchyChangedDetails& details);
 
@@ skipping 308 matching lines @@
   // Observers -------------------------------------------------------------
 
   base::ObserverList<ViewObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(View);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_VIEW_H_