Adds UMA for display color calibration in ChromeOS.

ui/display/display_constants.h

 // Copyright 2014 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 UI_DISPLAY_DISPLAY_CONSTANTS_H_
 #define UI_DISPLAY_DISPLAY_CONSTANTS_H_
 
 namespace ui {
 
 // Used to describe the state of a multi-display configuration.
@@ skipping 19 matching lines @@
 
 // Content protection methods applied on video output.
 enum OutputProtectionMethod {
   OUTPUT_PROTECTION_METHOD_NONE = 0,
   OUTPUT_PROTECTION_METHOD_HDCP = 1 << 0,
 };
 
 // HDCP protection state.
 enum HDCPState { HDCP_STATE_UNDESIRED, HDCP_STATE_DESIRED, HDCP_STATE_ENABLED };
 
-// Color calibration profiles.
+// Color calibration profiles. Don't change the order, and edit
+// tools/metrics/histograms/histograms.xml when a new item is added.
 enum ColorCalibrationProfile {
   COLOR_PROFILE_STANDARD,
   COLOR_PROFILE_DYNAMIC,
   COLOR_PROFILE_MOVIE,
   COLOR_PROFILE_READING,
+  NUM_COLOR_PROFILES,
 };
 
 }  // namespace ui
 
 #endif  // UI_DISPLAY_DISPLAY_CONSTANTS_H_