Web MIDI: add a new UMA entry for the final result code

media/midi/result.h

+// Copyright 2015 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 MEDIA_MIDI_RESULT_H_
+#define MEDIA_MIDI_RESULT_H_
+
+namespace media {
+namespace midi {
+
+// Result codes for MIDI.
+enum class Result {
+  NOT_INITIALIZED = 0,
+  OK,
+  NOT_SUPPORTED,
+  INITIALIZATION_ERROR,
+  // New code should be inserted here so that existing members keep the same
+  // assigned value. tools/metrics/histograms/histograms.xml contains Result
+  // enum entry, and it should be consistent with enum class Result.
+
+  // |MAX| is used in content/common/media/midi_messages.h with
+  // IPC_ENUM_TRAITS_MAX_VALUE macro. Keep the value up to date. Otherwise
+  // a new value can not be passed to the renderer.
+  MAX = INITIALIZATION_ERROR,
+};
+
+}  // namespace midi
+}  // namespace media
+
+#endif  // MEDIA_MIDI_RESULT_H_