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

third_party/WebKit/Source/modules/vr/VRPose.idl

Index: third_party/WebKit/Source/modules/vr/VRPose.idl
diff --git a/third_party/WebKit/Source/modules/vr/VRPose.idl b/third_party/WebKit/Source/modules/vr/VRPose.idl
index 097ca95d1b5b1469cc2d94dda49a070dd5b6c723..4b29a8474137115f41f729d5cabe87814b45f6c9 100644
--- a/third_party/WebKit/Source/modules/vr/VRPose.idl
+++ b/third_party/WebKit/Source/modules/vr/VRPose.idl
@@ -7,9 +7,9 @@
     OriginTrialEnabled=WebVR,
 ] interface VRPose {
     readonly attribute Float32Array? position;
-    readonly attribute Float32Array? linearVelocity;
-    readonly attribute Float32Array? linearAcceleration;
+    [MeasureAs=VRPoseLinearVelocity] readonly attribute Float32Array? linearVelocity;
+    [MeasureAs=VRPoseLinearAcceleration] readonly attribute Float32Array? linearAcceleration;
     readonly attribute Float32Array? orientation;
-    readonly attribute Float32Array? angularVelocity;
-    readonly attribute Float32Array? angularAcceleration;
+    [MeasureAs=VRPoseAngularVelocity] readonly attribute Float32Array? angularVelocity;
+    [MeasureAs=VRPoseAngularAcceleration] readonly attribute Float32Array? angularAcceleration;
 };