Allow customization of touch handler.

Add #setTouchHandler to PipManager so that other devices (e.g. TV,
Chrome OS) may set its own touch handler to overwrite the default one.

Bug: 148407130
Test: Set a custom touch handler, note it being used instead of the
default one

Change-Id: Ice3a57a700926b474b29dec1e0b3a8503501477b
3 files changed