Log the creation of a dialog boxes using DialogDelegate.

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 fd977cd937c355b53f9d48df75f27412effaa718..6af25ee59accfbcb26ef5379fe67751d4fff6cef 100644
--- a/ui/views/window/dialog_delegate.cc
+++ b/ui/views/window/dialog_delegate.cc
@@ -7,6 +7,7 @@
 #include <utility>
 
 #include "base/logging.h"
+#include "base/metrics/histogram_macros.h"
 #include "build/build_config.h"
 #include "ui/accessibility/ax_node_data.h"
 #include "ui/base/l10n/l10n_util.h"
@@ -31,7 +32,9 @@ namespace views {
 ////////////////////////////////////////////////////////////////////////////////
 // DialogDelegate:
 
-DialogDelegate::DialogDelegate() : supports_custom_frame_(true) {}
+DialogDelegate::DialogDelegate() : supports_custom_frame_(true) {
+  UMA_HISTOGRAM_BOOLEAN("Dialog.Delegate.Creation", true);
+}
 
 DialogDelegate::~DialogDelegate() {}