Adds UMA for display color calibration in ChromeOS.

ui/display/display_constants.h

Index: ui/display/display_constants.h
diff --git a/ui/display/display_constants.h b/ui/display/display_constants.h
index df0f1cc48069f1c7aaf18271cc649a65bc296496..7ad266495bd3e8d783f65ad5a4ae32db391f9e7a 100644
--- a/ui/display/display_constants.h
+++ b/ui/display/display_constants.h
@@ -37,12 +37,14 @@ enum OutputProtectionMethod {
 // 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