While at it, remove the notion of INTERNAL variables.

@caitp: Took some parts from your CL, since I was blocked on the temp scope bug.

R=mstarzinger@chromium.org
BUG=512574
LOG=N

Review URL: https://codereview.chromium.org/1250513004

Cr-Commit-Position: refs/heads/master@{#29812}