Add feature for helping apps track how they've been launched

Since Android apps can be opened from different places in many
different ways, it's useful to distinguish whether or not a user has
launched the app through its "front door" on the launcher. Add
AppLaunchChecker and a hasStartedFromLauncher method to determine and
persist this information.

Bug 27687726

Change-Id: Id5293c7124e62c102ca015f46063418a7768ec88
3 files changed