Adding WebVR interface to Blink

Source/modules/vr/PositionSensorVRDevice.idl

Index: Source/modules/vr/PositionSensorVRDevice.idl
diff --git a/Source/modules/vr/PositionSensorVRDevice.idl b/Source/modules/vr/PositionSensorVRDevice.idl
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+// Copyright 2015 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.
+
+// An PositionSensorVRDevice represents a user interface that provides an
+// orientation and position in space. This may be a Head Mounted Display or
+// any number of other six-degree-of-freedom devices that provide, for example,
+// hand tracking.
+// http://mozvr.github.io/webvr-spec/webvr.html#positionsensorvrdevice
+[
+    RuntimeEnabled=VRDevice,
+] interface PositionSensorVRDevice : VRDevice {
+    VRPositionState getState();
+    VRPositionState getImmediateState();
+    void resetSensor();
+};