Function to count dialog box creations.

chrome/browser/ui/views/dialog_uma/dialog_uma.h

+// Copyright 2017 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.
+
+#ifndef CHROME_BROWSER_UI_VIEWS_DIALOG_UMA_DIALOG_UMA_H_
+#define CHROME_BROWSER_UI_VIEWS_DIALOG_UMA_DIALOG_UMA_H_
+
+// Values used in the Dialog.Creation UMA metric. Each value represents a
+// different type of dialog box.
+// These values are written to logs. New enum values can be added, but existing
+// enums must never be renumbered or deleted and reused.
+enum class DialogIdentifier {
+  UNKNOWN = 0,
+  TRANSLATE = 1,
+  MAX_VALUE = 2,

[tapted, 2017/04/04 04:18:06]

This should drop the `= 2` and the trailing comma. The goal of trailing commas
is to avoid a `diff` on that line when someone appends something, but here
anything added should go _above_ this line rather than below it. So we actually
want to highlight this line if that's being violated (which we can do by
removing the trailing comma). And removing the =2 ensures it gets incremented
automatically by the compiler

[pdyson, 2017/04/04 04:29:53]

I see. Done.

With those changes "git cl format" put all of the enums on the same line. It
will go back to separate lines when I add more enums in the next cl.

+};
+
+// Record an UMA metric counting the creation of a dialog box of this type.
+void RecordDialogCreation(DialogIdentifier identifier);
+
+#endif  // CHROME_BROWSER_UI_VIEWS_DIALOG_UMA_DIALOG_UMA_H_