[Data Sharing] Check isAllowedToCreate for share sheet & TabGridDialog

I noticed there were two cases where isAllowedToCreate was not being
checked, but sharing could be started from. This should fix both of
them.

Bug: 360184707
Change-Id: Ife8876193651d9ba835b030fc4b3c39d7febbb89
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6194212
Auto-Submit: Calder Kitagawa <ckitagawa@chromium.org>
Commit-Queue: Calder Kitagawa <ckitagawa@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Hailey Wang <haileywang@google.com>
Cr-Commit-Position: refs/heads/main@{#1410484}