This CL is a prequisite for the stack machine changes, which will need
to use temporaries in various places due to the stack height requirements
on blocks.

R=ahaas@chromium.org,bradnelson@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2280063002
Cr-Commit-Position: refs/heads/master@{#39001}