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 c1b6ff05d2ad0753822bebe92ce174b44ac37200..82b3e0d0bd60e6fdcb3bc27712c1566467f7952e 100644
--- a/third_party/WebKit/Source/modules/vr/VRDisplay.h
+++ b/third_party/WebKit/Source/modules/vr/VRDisplay.h
@@ -131,7 +131,8 @@ class VRDisplay final : public EventTargetWithInlineData,
   void OnDeactivate(device::mojom::blink::VRDisplayEventReason) override;
 
   void OnVSync(device::mojom::blink::VRPosePtr,
-               mojo::common::mojom::blink::TimeDeltaPtr);
+               mojo::common::mojom::blink::TimeDeltaPtr,
+               int16_t frameId);
   void ConnectVSyncProvider();
 
   ScriptedAnimationController& ensureScriptedAnimationController(Document*);
@@ -147,6 +148,7 @@ 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;