Encode frame number in pixel data for pose sync

chrome/browser/android/vr_shell/vr_shell.h

Index: chrome/browser/android/vr_shell/vr_shell.h
diff --git a/chrome/browser/android/vr_shell/vr_shell.h b/chrome/browser/android/vr_shell/vr_shell.h
index 56b69dd659f377e3a73299d88845912b6b0aa24c..f8f935410a58e7e89541512b0f9413375f82bdae 100644
--- a/chrome/browser/android/vr_shell/vr_shell.h
+++ b/chrome/browser/android/vr_shell/vr_shell.h
@@ -73,6 +73,7 @@ class VrShell : public device::GvrDelegate {
   void UpdateWebVRTextureBounds(
       int eye, float left, float top, float width, float height) override;
   gvr::GvrApi* gvr_api() override;
+  void SetGvrPoseForWebVr(gvr::Mat4f pose, uint32_t pose_num) override;
 
   void ContentSurfaceChanged(
       JNIEnv* env,
@@ -156,6 +157,12 @@ class VrShell : public device::GvrDelegate {
   bool webvr_mode_ = false;
   bool webvr_secure_origin_ = false;
   int64_t webvr_warning_end_nanos_ = 0;
+  // The pose queue size must be a power of two to avoid glitches when
+  // the pose counter wraps around. Should be large enough to handle
+  // the current backlog of poses which is 2-3 frames.
+  static constexpr int POSE_QUEUE_SIZE = 8;
+  gvr::Mat4f webvr_head_pose_[POSE_QUEUE_SIZE];
+  int32_t webvr_newest_pose_num_ = 0;
 
   base::WeakPtrFactory<VrShell> weak_ptr_factory_;