UMA stats for stylus usage

ash/shared/app_types.h

Index: ash/shared/app_types.h
diff --git a/ash/shared/app_types.h b/ash/shared/app_types.h
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+++ b/ash/shared/app_types.h
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+// Copyright 2016 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 ASH_SHARED_APP_TYPES_H_
+#define ASH_SHARED_APP_TYPES_H_
+
+namespace ash {
+
+// App type of the window. This enum is used to back
+// an UMA histogram and should be treated as append-only.
+enum class AppType {
+  OTHERS = 0,
+  BROWSER,
+  CHROME_APP,
+  ARC_APP,
+  DEFAULT_NOTE_TAKING_APP,
+  APP_TYPE_LAST = DEFAULT_NOTE_TAKING_APP,
+};
+
+const int kAppCount = static_cast<int>(AppType::APP_TYPE_LAST) + 1;
+
+}  // namespace ash
+
+#endif  // ASH_SHARED_APP_TYPES_H_