Encode frame number in pixel data for pose sync

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;
   float leftDegrees;
   float rightDegrees;
 };
 
 // A display's position, orientation, velocity, and acceleration state at the
 // given timestamp.
 struct VRPose {
   double timestamp;
   array<float, 4>? orientation;
   array<float, 3>? position;
   array<float, 3>? angularVelocity;
   array<float, 3>? linearVelocity;
   array<float, 3>? angularAcceleration;
   array<float, 3>? linearAcceleration;
+  // The poseIndex is a sequential ID that's incremented on each distinct
+  // getPose result, it may wrap around for long sessions.
+  uint32 poseIndex;
 };
 
 struct VRDisplayCapabilities {
   bool hasOrientation;
   bool hasPosition;
   bool hasExternalDisplay;
   bool canPresent;
 };
 
 // Information about the optical properties for an eye in a VRDisplay.
@@ skipping 39 matching lines @@
   SubmitFrame(uint32 index, VRPose? pose);
   UpdateLayerBounds(uint32 index, VRLayerBounds leftBounds, VRLayerBounds rightBounds);
 };
 
 interface VRServiceClient {
   OnDisplayChanged(VRDisplay display);
   OnExitPresent(uint32 index);
   OnDisplayConnected(VRDisplay display);
   OnDisplayDisconnected(uint32 index);
 };