WebXR samples: fix cottontail dirty state propagation

Copying a node's children happened asynchronously, resulting in
them getting inconsistent worldMatrixDirty values and objects
being rendered at the wrong place.

Change-Id: If5bd6f166f24eabbcb628f70fba8f01b5a810490
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1907274
Auto-Submit: Klaus Weidner <klausw@chromium.org>
Reviewed-by: Piotr Bialecki <bialpio@chromium.org>
Commit-Queue: Piotr Bialecki <bialpio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713992}
1 file changed