Two minor cleanups in pattern rewriter

Two minor cleanups in pattern rewriter

- No need to call AsVariableProxy() on a VariableProxy
- Reduce AST visitor boilerplate using pre-existing macro
  (and re-alphabetize the list of non-patterns).

R=littledan@chromium.org

Committed: https://crrev.com/c2c6323218ecdd30d8b1ed304c69d7643612fe85
Cr-Commit-Position: refs/heads/master@{#31032}

[Dan Ehrenberg, 2015-09-30 19:53:54]

lgtm

[adamk, 2015-09-30 19:56:15]

The CQ bit was checked by adamk@chromium.org

[commit-bot: I haz the power, 2015-09-30 19:56:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1376633005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1376633005/1

[commit-bot: I haz the power, 2015-09-30 20:22:33]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-30 20:22:53]

Patchset 1 (id:??) landed as
https://crrev.com/c2c6323218ecdd30d8b1ed304c69d7643612fe85
Cr-Commit-Position: refs/heads/master@{#31032}