Re-land^2 WebVR compositor bypass via BrowserMain context + mailbox

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 2af38f579633e856444ee7611122b8e7cb1118eb..098c8b9e73e73ffe4c94650b4b0d9091e5630e82 100644
--- a/device/vr/vr_service.mojom
+++ b/device/vr/vr_service.mojom
@@ -5,6 +5,8 @@
 module device.mojom;
 
 import "mojo/common/time.mojom";
+import "gpu/ipc/common/mailbox.mojom";
+import "gpu/ipc/common/sync_token.mojom";
 
 // A field of view, given by 4 degrees describing the view from a center point.
 struct VRFieldOfView {
@@ -24,6 +26,10 @@ struct VRPose {
   array<float, 3>? linearVelocity;
   array<float, 3>? angularAcceleration;
   array<float, 3>? linearAcceleration;
+  int32 surfaceId;
+  int32 frameId;
+  gpu.mojom.Mailbox? mailbox;
+//  gpu.mojom.SyncToken syncToken;
 };
 
 struct VRDisplayCapabilities {