Write mojom and EnumTraits for display::HDCPState.

ui/display/mojo/display_struct_traits_test.mojom

 // 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.
 
 module display.mojom;
 
 import "ui/display/mojo/display.mojom";
+import "ui/display/mojo/display_constants.mojom";
 import "ui/display/mojo/display_layout.mojom";
 import "ui/display/mojo/display_mode.mojom";
 import "ui/display/mojo/display_snapshot_mojo.mojom";
 import "ui/display/mojo/gamma_ramp_rgb_entry.mojom";
 
 interface DisplayStructTraitsTest {
   [Sync]
   EchoDisplay(Display in) => (Display out);
 
   [Sync]
   EchoDisplayMode(DisplayMode in) => (DisplayMode out);
 
   [Sync]
   EchoDisplaySnapshotMojo(DisplaySnapshotMojo in) => (DisplaySnapshotMojo
     out);
 
   [Sync]
   EchoDisplayPlacement(DisplayPlacement in) => (DisplayPlacement out);
 
   [Sync]
   EchoDisplayLayout(DisplayLayout in) => (DisplayLayout out);
 
   [Sync]
+  EchoHDCPState(HDCPState in) => (HDCPState out);
+
+  [Sync]
   EchoGammaRampRGBEntry(GammaRampRGBEntry in) => (GammaRampRGBEntry out);
 };