Summary:
We need it to stop repeating to commit new shadow tree in `ShadowTree::commit` when a transaction cancels the commit.
Changelog: [Internal] Fabric-specific internal change.
Reviewed By: JoshuaGross, sammy-SC
Differential Revision: D23603959
fbshipit-source-id: d279fb3bf4190e860740a6450595d6f2fc3117f7