Custom Tab: Add ability to add menu items

[pocmo]

User story: mozilla-mobile/reference-browser#209

CustomTabsIntent.Builder.addMenuItem()

This may require changes to our menu/toolbar component too.

┆Issue is synchronized with this Jira Task

[jonalmeida]

This may require changes to our menu/toolbar component too.

It does! 😄

Simply adding menu items to the menu builder persists them for the lifetime of the application since the menu builder lives in the Components. My naive implementation that I have is to hold on to a list of menu items we add to the menu, and in stop we filter out the menu items and pass it back to the menu builder.

So far it seems to work, but it doesn't feel right. I had an older patch that added a 'tag' attribute for menu items so that we could give a tag to the CT items and filter them out easily.

@pocmo would the latter solution work? I recall you wanted to do some work with adding ids to menu items, but I'm hoping this solution doesn't overlap.

[pocmo]

Modifying the global configuration for the menu sounds dangerous and may introduces weird races while switching between custom tabs and the actual browser screen.

I'd prefer if we either have two builders (one for the normal menu) and one for custom tabs (that gets build dynamically with CustomTabConfig as input) OR a way to build on top of the existing builder which basically creates a copy and attaches some additional items (e.g. menuBuilder = components.menuBuilder + something(CustomTabConfig)).

Currently we assign the menu builder to the toolbar ourselves (in BrowserFragment). Maybe this could happen inside a feature and then the feature can decide what to do.