Plugins may want to disable or otherwise modify actions, for example to
remove the Cherry-Pick action in the UI so that users are encouraged to
use an external tool.
Add an extension point that visits each ActionInfo before it's added to
the map. The visitor receives a mutable ActionInfo as well as defensive
copies of the change and revision info.
Bug: Issue 4764
Change-Id: Ie83d7910947ad3d0640aa72e891cfc513ff89fd4
f1790ce471