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

device/vr/test/fake_vr_device.h

Index: device/vr/test/fake_vr_device.h
diff --git a/device/vr/test/fake_vr_device.h b/device/vr/test/fake_vr_device.h
index 1d40bfafbf6f5113904d4372e7a459a15880a5d4..fcfbbef2af6d4b9c766dc8c93f993d00887dea15 100644
--- a/device/vr/test/fake_vr_device.h
+++ b/device/vr/test/fake_vr_device.h
@@ -31,7 +31,8 @@ class FakeVRDevice : public VRDevice {
   void SetSecureOrigin(bool secure_origin) override;
   void ExitPresent() override;
   void SubmitFrame(mojom::VRPosePtr pose) override;
-  void UpdateLayerBounds(mojom::VRLayerBoundsPtr leftBounds,
+  void UpdateLayerBounds(int16_t frame_index,
+                         mojom::VRLayerBoundsPtr leftBounds,
                          mojom::VRLayerBoundsPtr rightBounds) override;
   void GetVRVSyncProvider(mojom::VRVSyncProviderRequest request) override;