[ReferenceTarget] Add field to ShadowInit dict
Add a field to ShadowInit dict that can be used to set referenceTarget
upon creation of a new ShadowRoot.
Bug: 353750121
Change-Id: If122fd64a77793b7cbe7a6f6bce860c2e402637c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5829611
Commit-Queue: Dan Clark daniec@microsoft.com
Reviewed-by: Mason Freed masonf@chromium.org
Cr-Commit-Position: refs/heads/main@{#1350348}