Add View::AddedToWidget and RemovedFromWidget.

ui/views/view.cc

 // 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.
 
 #define _USE_MATH_DEFINES // For VC++ to get M_PI. This has to be first.
 
 #include "ui/views/view.h"
 
 #include <algorithm>
 #include <cmath>
@@ skipping 1498 matching lines @@
 void View::NativeViewHierarchyChanged() {
   FocusManager* focus_manager = GetFocusManager();
   if (accelerator_focus_manager_ != focus_manager) {
     UnregisterAccelerators(true);
 
     if (focus_manager)
       RegisterPendingAccelerators();
   }
 }
 
+void View::AddedToWidget() {}
+
+void View::RemovedFromWidget() {}
+
 // Painting --------------------------------------------------------------------
 
 void View::PaintChildren(const ui::PaintContext& context) {
   TRACE_EVENT1("views", "View::PaintChildren", "class", GetClassName());
   View::Views children = GetChildrenInZOrder();
   DCHECK_EQ(child_count(), static_cast<int>(children.size()));
   for (auto* child : children) {
     if (!child->layer())
       child->Paint(context);
   }
@@ skipping 476 matching lines @@
       // added to the view hierarchy.
       if (GetFocusManager())
         RegisterPendingAccelerators();
     } else {
       if (details.child == this)
         UnregisterAccelerators(true);
     }
   }
 
   ViewHierarchyChanged(details);
+
+  if (details.is_add) {
+    const auto widget = GetWidget();
+    if (widget != nullptr && widget != attached_widget_) {
+      attached_widget_ = widget;
+      AddedToWidget();
+    }
+  } else if (details.child == this) {
+    if (attached_widget_) {
+      RemovedFromWidget();
+      attached_widget_ = nullptr;
+    }
+  }
+
   details.parent->needs_layout_ = true;
 }
 
 void View::PropagateNativeThemeChanged(const ui::NativeTheme* theme) {
   if (native_theme_ && native_theme_ != theme)
     return;
 
   {
     internal::ScopedChildrenLock lock(this);
     for (auto* child : children_)
@@ skipping 526 matching lines @@
   // Message the RootView to do the drag and drop. That way if we're removed
   // the RootView can detect it and avoid calling us back.
   gfx::Point widget_location(event.location());
   ConvertPointToWidget(this, &widget_location);
   widget->RunShellDrag(this, data, widget_location, drag_operations, source);
   // WARNING: we may have been deleted.
   return true;
 }
 
 }  // namespace views