Log the creation of dialog boxes using DialogDelegateView and BubbleDialogDelegateView.

ui/views/window/dialog_delegate.cc

Index: ui/views/window/dialog_delegate.cc
diff --git a/ui/views/window/dialog_delegate.cc b/ui/views/window/dialog_delegate.cc
index d354353c5db90c32b7bd1c53d52e5c4e3b7d99d3..0c62cdc196e4a9d1f73043559a94e861585a9c5b 100644
--- a/ui/views/window/dialog_delegate.cc
+++ b/ui/views/window/dialog_delegate.cc
@@ -243,6 +243,7 @@ ui::AXRole DialogDelegate::GetAccessibleWindowRole() const {
 DialogDelegateView::DialogDelegateView() {
   // A WidgetDelegate should be deleted on DeleteDelegate.
   set_owned_by_client();
+  UMA_HISTOGRAM_BOOLEAN("Dialog.DialogDelegateView.Create", true);
 }
 
 DialogDelegateView::~DialogDelegateView() {}