Write mojom and EnumTraits for display::HDCPState.

ui/display/mojo/display_constants.mojom

 // 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.
 
 module display.mojom;
 
 // Corresponding to display::DisplayConnectionType.
 enum DisplayConnectionType {
   DISPLAY_CONNECTION_TYPE_NONE = 0,
   DISPLAY_CONNECTION_TYPE_UNKNOWN = 1,
   DISPLAY_CONNECTION_TYPE_INTERNAL = 2,
   DISPLAY_CONNECTION_TYPE_VGA = 4,
   DISPLAY_CONNECTION_TYPE_HDMI = 8,
   DISPLAY_CONNECTION_TYPE_DVI = 16,
   DISPLAY_CONNECTION_TYPE_DISPLAYPORT = 32,
   DISPLAY_CONNECTION_TYPE_NETWORK = 64,
   DISPLAY_CONNECTION_TYPE_VIRTUAL = 128,
 };
+
+// Corresponding to display::HDCPState.
+enum HDCPState {
+  HDCP_STATE_UNDESIRED,
+  HDCP_STATE_DESIRED,
+  HDCP_STATE_ENABLED,
+};