Add Brightness setting for VR Mode.

This change saves and loads a different brightness setting when the user
goes in and out of VR Mode.

Bug: 30984614
Change-Id: If3c3e81b592e0c6fd037e5783559683e5cb58379
diff --git a/proto/src/metrics_constants.proto b/proto/src/metrics_constants.proto
index 20cca8e..ff3a9c5 100644
--- a/proto/src/metrics_constants.proto
+++ b/proto/src/metrics_constants.proto
@@ -2219,6 +2219,12 @@
     // OS: N-MR2
     ACTION_LOCK_BECAUSE_SIM_REMOVED = 497;
 
+    // ACTION: QS Brightness Slider (with auto brightness disabled, and VR enabled)
+    //   SUBTYPE: slider value
+    // CATEGORY: QUICK_SETTINGS
+    // OS: 6.0
+    ACTION_BRIGHTNESS_FOR_VR = 498;
+
     // ACTION: A captive portal was detected during network validation
     // CATEGORY: NOTIFICATION
     // OS: N-MR2