Allow VRDisplay to specify which frame the layer bounds should be updated at.

device/vr/vr_display_impl.h

Index: device/vr/vr_display_impl.h
diff --git a/device/vr/vr_display_impl.h b/device/vr/vr_display_impl.h
index 1e52a6ec094290e4ba211c4ae17b1ca490251e6f..02a1e1a17c9f2022f6ed1ea416fb09910b6a8e68 100644
--- a/device/vr/vr_display_impl.h
+++ b/device/vr/vr_display_impl.h
@@ -36,7 +36,8 @@ class VRDisplayImpl : public mojom::VRDisplay {
   void ExitPresent() override;
   void SubmitFrame(mojom::VRPosePtr pose) override;
 
-  void UpdateLayerBounds(mojom::VRLayerBoundsPtr left_bounds,
+  void UpdateLayerBounds(int16_t frame_index,
+                         mojom::VRLayerBoundsPtr left_bounds,
                          mojom::VRLayerBoundsPtr right_bounds) override;
   void GetVRVSyncProvider(mojom::VRVSyncProviderRequest request) override;