Isolate a presenting VR device from pages other than the one presenting.

device/vr/vr_device.cc

 // 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.
 
 #include "device/vr/vr_device.h"
 #include "device/vr/vr_device_provider.h"
 
 namespace device {
 
 unsigned int VRDevice::next_id_ = 1;
 
 VRDevice::VRDevice(VRDeviceProvider* provider)
     : provider_(provider), id_(next_id_) {
   // Prevent wraparound. Devices with this ID will be treated as invalid.
   if (next_id_ != VR_DEVICE_LAST_ID)
     next_id_++;
 }
 
 VRDevice::~VRDevice() {}
 
+bool VRDevice::RequestPresent() {
+  return true;
+};
+
 }  // namespace device