gn format: Make parenthesizing better

gn format: Make parenthesizing better

- Fixes one bug (the precedence of suffix vs. unary did not match parsing)
- Adds "redundant" parentheses in the case of && and || because they're
otherwise too confusing to read.

R=brettw@chromium.org
BUG=348474
Committed: https://crrev.com/3e2c7b0b7caaa0cc28eff1d3726b1c34f6c150fe
Cr-Commit-Position: refs/heads/master@{#306282}

[brettw, 2014-12-01 22:32:18]

lgtm

[scottmg, 2014-12-01 22:50:51]

The CQ bit was checked by scottmg@chromium.org

[commit-bot: I haz the power, 2014-12-01 22:52:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/772663002/1

[commit-bot: I haz the power, 2014-12-01 22:55:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-01 22:56:21]

Patchset 1 (id:??) landed as
https://crrev.com/3e2c7b0b7caaa0cc28eff1d3726b1c34f6c150fe
Cr-Commit-Position: refs/heads/master@{#306282}