GitLab

To more closely align with mocks hide separator before expand.
This prevents the two separators from overlapping when the expand
occurs.

Bug: 1148692
Change-Id: I3b0254b2da65d14907d0260c2e600f1bc8cf39c0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2574569Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Commit-Queue: Melissa Zhang <melzhang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834417}