This CL adds a new public API to allow Connections
to start an activity on top of the in-call UI.
The Connection passes a PendingIntent to Telecomm which
then forwards it on to InCallUI. The Connection can cancel
the operation by calling PendingIntent.cancel().
This allows services like SIP and Hangouts to show dialogs
to the user when making a call.
Change-Id: I65119a89c925a93467d1b27304ffec9b088b172f
2ab88cc313