Adds ContextMenu handling to ActivityServicePresentation

This adds a new delegate method to ActivityServicePresentation
protocol so ActivityServiceController can ask "presentation"
delegate to show a Context Menu with a title and an array of
menu items as options.

For example, -showActivityServiceContextMenu:items: can be called
like this:

[delegate showActivityServiceContextMenu:@"Fruits?" items:@[
  [[ContextMenuItem alloc] initWithTitle:@"Apples" action:^{}],
  [[ContextMenuItem alloc] initWithTitle:@"Oranges" action:^{}]
]];


Change-Id: I7aa28d2616b36be0b43a331e771b950ea3c92f9a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1618046
Commit-Queue: Peter Lee <pkl@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662636}
7 files changed