Reland r256396 Add views implementation for AXTreeSource.

ui/views/widget/widget.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.
 
 #include "ui/views/widget/widget.h"
 
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 409 matching lines @@
 void Widget::ViewHierarchyChanged(
     const View::ViewHierarchyChangedDetails& details) {
   if (!details.is_add) {
     if (details.child == dragged_view_)
       dragged_view_ = NULL;
     FocusManager* focus_manager = GetFocusManager();
     if (focus_manager)
       focus_manager->ViewRemoved(details.child);
     ViewStorage::GetInstance()->ViewRemoved(details.child);
     native_widget_->ViewRemoved(details.child);
+
+    // Many observers do not remove themselves during destruction, so we must
+    // not notify once we destroy our |root_view_|.
+    if (root_view_.get()) {
+      FOR_EACH_OBSERVER(
+          WidgetObserver, observers_, OnViewRemoved(this, details.child));
+    }
   }
 }
 
 void Widget::NotifyNativeViewHierarchyWillChange() {
   FocusManager* focus_manager = GetFocusManager();
   // We are being removed from a window hierarchy.  Treat this as
   // the root_view_ being removed.
   if (focus_manager)
     focus_manager->ViewRemoved(root_view_.get());
 }
@@ skipping 998 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 // internal::NativeWidgetPrivate, NativeWidget implementation:
 
 internal::NativeWidgetPrivate* NativeWidgetPrivate::AsNativeWidgetPrivate() {
   return this;
 }
 
 }  // namespace internal
 }  // namespace views