Extensions: Make PermissionMessages a vector instead of list

This should be slightly more efficient, and resolves a 3+-year-old TODO
assigned to me.

Bug: none
Change-Id: I641d0e2c076f90cd76a102a725ae4df994cbf3c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1611929
Auto-Submit: Marc Treib <treib@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660185}
2 files changed