base

Allow multiple range selections using the shift key.

- Introduce an API on MultiSelectManager for starting/ending range
  selections.

- Navigation with the shift key pressed extends the current range
  selection (or starts a new one, if one isn't in progress).

- Navigation without the shift key pressed will end the current range
  selection.

BUG=27124371

Change-Id: Ieddf3ee816812bf5210463536fe63179ef1809ad
(cherry picked from commit 09792ef1506f4cbd944e16651508be435d92c5be)