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

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

 // Copyright 2016 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.
 
 enum VREye {
     "left",
     "right"
 };
 
 // https://w3c.github.io/webvr/#interface-vrdisplay
 [
     ActiveScriptWrappable,
     DependentLifetime,
     OriginTrialEnabled=WebVR
 ] interface VRDisplay : EventTarget {
     // An identifier for this device unique across VRDisplays.
     readonly attribute unsigned long displayId;
 
     // A user-readable name identifying the device.
-    readonly attribute DOMString displayName;
+    [MeasureAs=VRDisplayDisplayName] readonly attribute DOMString displayName;
 
-    readonly attribute boolean isConnected;
+    [MeasureAs=VRDisplayIsConnected] readonly attribute boolean isConnected;
     readonly attribute boolean isPresenting;
 
     // [Constant]?
     readonly attribute VRDisplayCapabilities capabilities;
 
     readonly attribute VRStageParameters stageParameters;
 
     boolean getFrameData(VRFrameData frameData);
     [DeprecateAs=VRDeprecatedGetPose] VRPose getPose();
-    void resetPose();
+    [MeasureAs=VRDisplayResetPose] void resetPose();
 
     attribute double depthNear;
     attribute double depthFar;
 
     VREyeParameters getEyeParameters(VREye whichEye);
 
     long requestAnimationFrame(FrameRequestCallback callback);
     void cancelAnimationFrame(long handle);
 
     // Begin presenting to the VRDisplay. Must be called in response to a user gesture.
     // Repeat calls while already presenting will update the VRLayer being displayed.
     [CallWith=ScriptState] Promise requestPresent(sequence<VRLayer> layers);
 
     // Stops presenting to the VRDisplay.
     [CallWith=ScriptState] Promise exitPresent();
 
     // Get the sources currently being presented.
     sequence<VRLayer> getLayers();
 
     // The VRLayer provided to the `VRDisplay` will be captured and presented
     // in the HMD. Calling this function has the same effect on the source
     // canvas as any other operation that uses its source image, and canvases
     // created without preserveDrawingBuffer set to true will be cleared.
     void submitFrame();
 };