GitLab

Added a GetPermissions() method to APIPermissions, which returns the
PermissionIDSet for that API permission. This will be used for the new
permission messages system, which can generate
CoalescedPermissionMessages from these permissions.

BUG=398257

Review URL: https://codereview.chromium.org/795543002

Cr-Commit-Position: refs/heads/master@{#308034}