Add UseCounters to evaluate usage and risk with upcoming WebVR spec changes.

third_party/WebKit/Source/core/frame/UseCounter.h

Index: third_party/WebKit/Source/core/frame/UseCounter.h
diff --git a/third_party/WebKit/Source/core/frame/UseCounter.h b/third_party/WebKit/Source/core/frame/UseCounter.h
index ed7341c493a69b2a960beaa85d8c9ce2dc1a9b4c..4eda6c26dbad7846d26ef137b31e1512ff65cb73 100644
--- a/third_party/WebKit/Source/core/frame/UseCounter.h
+++ b/third_party/WebKit/Source/core/frame/UseCounter.h
@@ -1478,6 +1478,15 @@ class CORE_EXPORT UseCounter {
     HTMLMediaElementControlsListNoFullscreen = 1855,
     HTMLMediaElementControlsListNoRemotePlayback = 1856,
     PointerEventClickRetargetCausedByCapture = 1857,
+    VRDisplayIsConnected = 1858,
+    VRDisplayResetPose = 1859,
+    VRDisplayCapabilitiesHasOrientation = 1860,
+    VRDisplayDisplayName = 1861,
+    VREyeParametersOffset = 1862,
+    VRPoseLinearVelocity = 1863,
+    VRPoseLinearAcceleration = 1864,
+    VRPoseAngularVelocity = 1865,
+    VRPoseAngularAcceleration = 1866,
 
     // Add new features immediately above this line. Don't change assigned
     // numbers of any item, and don't reuse removed slots.