- Add info.targetElementId to menus.onShown event.
- Add info.targetElementId to menus.onClicked event.
- Add menus.getTargetElement API that is available to all contexts,
including content scripts, which allows extensions to get the DOM
element for a given targetElementId.
- Add new schema instead of re-using schemas/menus.json to avoid sending
too much schema data (of the existing menus API) to content processes.
MozReview-Commit-ID: 6Onf7jZlIho
