GitLab

This CL enables the scrollable shelf to show context menu for proper
gestures (like long-time tapping). It helps to keep the UI consistency
with the shelf view.

Bug: 1003584
Change-Id: I74b69ffea84fedc6c780cacc01b6eea680b6875b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1801320Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Andrew Xu <andrewxu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697036}