Remove Sync GetPose VRService call, implement VRVSyncProvider

device/vr/vr_service.mojom

Index: device/vr/vr_service.mojom
diff --git a/device/vr/vr_service.mojom b/device/vr/vr_service.mojom
index d41b1a9ed09da0fe5157c51d9de5af058d4e1a0d..e401917f1f2c6e222421eed73844ec85247b2c3f 100644
--- a/device/vr/vr_service.mojom
+++ b/device/vr/vr_service.mojom
@@ -84,8 +84,6 @@ interface VRServiceClient {
 };
 
 interface VRDisplay {
-  [Sync]
-  GetPose() => (VRPose? pose);
   ResetPose();
 
   RequestPresent(bool secureOrigin) => (bool success);
@@ -94,6 +92,12 @@ interface VRDisplay {
   UpdateLayerBounds(VRLayerBounds leftBounds, VRLayerBounds rightBounds);
 };
 
+interface VRVSyncProviderClient {
+  // VRVSyncProviders should ensure the callback from OnVSync is run before sending another OnVSync
+  // to avoid having multiple VSyncs queue up in the case of a slow client.
+  OnVSync(VRPose? pose, double time_seconds) => ();
+};
+
 interface VRDisplayClient {
   OnChanged(VRDisplayInfo display);
   OnExitPresent();
@@ -101,4 +105,5 @@ interface VRDisplayClient {
   OnFocus();
   OnActivate(VRDisplayEventReason reason);
   OnDeactivate(VRDisplayEventReason reason);
+  OnVRVsyncProviderReady() => (VRVSyncProviderClient client);
 };