Log the creation of a dialog boxes using DialogDelegate.

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"
 #include "build/build_config.h"
 #include "ui/accessibility/ax_node_data.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/gfx/color_palette.h"
 #include "ui/strings/grit/ui_strings.h"
 #include "ui/views/bubble/bubble_border.h"
 #include "ui/views/bubble/bubble_frame_view.h"
 #include "ui/views/controls/button/label_button.h"
 #include "ui/views/layout/layout_constants.h"
 #include "ui/views/layout/layout_provider.h"
 #include "ui/views/style/platform_style.h"
 #include "ui/views/widget/widget.h"
 #include "ui/views/widget/widget_observer.h"
 #include "ui/views/window/dialog_client_view.h"
 
 #if defined(OS_WIN)
 #include "ui/base/win/shell.h"
 #endif
 
 namespace views {
 
 ////////////////////////////////////////////////////////////////////////////////
 // DialogDelegate:
 
-DialogDelegate::DialogDelegate() : supports_custom_frame_(true) {}
+DialogDelegate::DialogDelegate() : supports_custom_frame_(true) {
+  UMA_HISTOGRAM_BOOLEAN("Dialog.Delegate.Creation", true);

[msw, 2017/05/01 21:51:30]

Why BOOLEAN? Shouldn't this be UMA_HISTOGRAM_COUNTS_*?

[jwd, 2017/05/03 20:14:40]

No, it's confusing naming. UMA_HISTOGRAM_COUNTS_* is for logging a count of
something, like number of vowels on a page. It would let you answer questions
like "how many pages were seen with >100 vowels" or more abstractly, "how many
times a range of count values were logged". 

BOOLEAN is a special case of an enum histogram. It's for logging an event, like
a vowel was seen. It will just let you answer "how many vowels were seen".

In this case BOOLEAN is the correct histogram.

[msw, 2017/05/03 22:53:22]

Acknowledged.

+}
 
 DialogDelegate::~DialogDelegate() {}
 
 // static
 Widget* DialogDelegate::CreateDialogWidget(WidgetDelegate* delegate,
                                            gfx::NativeWindow context,
                                            gfx::NativeView parent) {
   views::Widget* widget = new views::Widget;
   views::Widget::InitParams params =
       GetDialogWidgetInitParams(delegate, context, parent, gfx::Rect());
@@ skipping 216 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