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

device/vr/vr_service.mojom

 // 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.
 
 module device;
 
 // A field of view, given by 4 degrees describing the view from a center point.
 struct VRFieldOfView {
   float upDegrees;
   float downDegrees;
@@ skipping 48 matching lines @@
    float top;
    float width;
    float height;
 };
 
 interface VRService {
   SetClient(VRServiceClient client);
 
   GetDisplays() => (array<VRDisplay> displays);
   [Sync]
-  GetPose(uint32 index) => (VRPose pose);
+  GetPose(uint32 index) => (VRPose? pose);
   ResetPose(uint32 index);
 
-  RequestPresent(uint32 index);
+  RequestPresent(uint32 index) => (bool success);
   ExitPresent(uint32 index);
-  SubmitFrame(uint32 index);
+  SubmitFrame(uint32 index, VRPose pose);
   UpdateLayerBounds(uint32 index, VRLayerBounds leftBounds, VRLayerBounds rightBounds);
 };
 
 interface VRServiceClient {
   OnDisplayChanged(VRDisplay display);
+  OnExitPresent(uint32 index);
 };