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

third_party/WebKit/Source/modules/vr/VRDisplay.h

Index: third_party/WebKit/Source/modules/vr/VRDisplay.h
diff --git a/third_party/WebKit/Source/modules/vr/VRDisplay.h b/third_party/WebKit/Source/modules/vr/VRDisplay.h
index 4f15fe6be2c1f907c2a8ac51130dae94141bf115..64f8809e0ca24bcdb31597ba04bd15b954b5ba0a 100644
--- a/third_party/WebKit/Source/modules/vr/VRDisplay.h
+++ b/third_party/WebKit/Source/modules/vr/VRDisplay.h
@@ -131,7 +131,9 @@ class VRDisplay final : public EventTargetWithInlineData,
   void OnActivate(device::mojom::blink::VRDisplayEventReason) override;
   void OnDeactivate(device::mojom::blink::VRDisplayEventReason) override;
 
-  void OnVSync(device::mojom::blink::VRPosePtr, double timeSeconds);
+  void OnVSync(device::mojom::blink::VRPosePtr,
+               double timeSeconds,
+               int16_t frameId);
   void OnVSyncProviderDisconnected();
   void ConnectVSyncProvider();
 
@@ -148,6 +150,7 @@ class VRDisplay final : public EventTargetWithInlineData,
   Member<VREyeParameters> m_eyeParametersLeft;
   Member<VREyeParameters> m_eyeParametersRight;
   device::mojom::blink::VRPosePtr m_framePose;
+  int16_t m_frameId;
   VRLayer m_layer;
   double m_depthNear = 0.01;
   double m_depthFar = 10000.0;