Log the creation of dialog boxes using DialogDelegateView and BubbleDialogDelegateView.

ui/views/window/dialog_delegate.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/window/dialog_delegate.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "base/metrics/histogram_macros.h"
@@ skipping 221 matching lines @@
 ui::AXRole DialogDelegate::GetAccessibleWindowRole() const {
   return ui::AX_ROLE_DIALOG;
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // DialogDelegateView:
 
 DialogDelegateView::DialogDelegateView() {
   // A WidgetDelegate should be deleted on DeleteDelegate.
   set_owned_by_client();
+  UMA_HISTOGRAM_BOOLEAN("Dialog.DelegateView.Creation", true);
 }
 
 DialogDelegateView::~DialogDelegateView() {}
 
 void DialogDelegateView::DeleteDelegate() {
   delete this;
 }
 
 Widget* DialogDelegateView::GetWidget() {
   return View::GetWidget();
@@ skipping 12 matching lines @@
   node_data->role = ui::AX_ROLE_DIALOG;
 }
 
 void DialogDelegateView::ViewHierarchyChanged(
     const ViewHierarchyChangedDetails& details) {
   if (details.is_add && details.child == this && GetWidget())
     NotifyAccessibilityEvent(ui::AX_EVENT_ALERT, true);
 }
 
 }  // namespace views