Hide floating toolbar when user interacts with screen.

- Adds an ActionMode.snooze(int) API.
- Clients call this to hide the floating toolbar on DOWN touch event.
- This is called repeatedly as a snooze timeout will re-show the
  toolbar.
- ActionMode.snooze(0) will "wake" the toolbar, reshowing it.
- Clients call this to re-show the toolbar on UP touch event.
- This CL also adds code to hide the toolbar when the "content rect"
  is changing.

Bug: 20148125
Change-Id: If5a9a15f72c73cad8ca01a4328a58570b3e29f66