add UMA metrics for voice interaction entries.

ash/metrics/voice_interaction_metrics.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 ASH_METRICS_VOICE_INTERACTION_METRICS_H_
+#define ASH_METRICS_VOICE_INTERACTION_METRICS_H_
+
+namespace ash {
+
+enum class VoiceInteractionMetaLayerEntry {

[Daniel Erat, 2017/05/23 22:32:18]

i think it would make more sense to record these as user actions than
histograms. this is what we use for other accelerators. see e.g.
Accel_Focus_Search, Accel_Search_LWin, etc.

[Muyuan, 2017/05/24 00:24:54]

Acknowledged. Uploaded a patch set to use user action

+  META_SHIFT_A = 0,
+  // Note: add items immediately above this line.
+  COUNT
+};
+
+enum class VoiceInteractionEntry {
+  META_A = 0,
+  META_SPACE,
+  LONG_PRESS_APP_LIST_BUTTON,
+  // Note: add items immediately above this line.
+  COUNT
+};
+
+}  // namespace ash
+
+#endif  // ASH_METRICS_VOICE_INTERACTION_METRICS_H_