Remove #pragma once. Just from base/ for now.

Remove #pragma once.  Just from base/ for now.

Done with
  git grep -l --cached 'pragma once' | xargs sed -i '/^#pragma once.*/d'

Followed up with a manual inspection of the result of
  git grep -l --cached 'pragma once'.

For context:
  https://groups.google.com/a/chromium.org/forum/?fromgroups#!topic/chromium-dev/RMcVNGjB4II

[brettw, 2012-07-11 04:56:45]

lgtm

[commit-bot: I haz the power, 2012-07-11 05:21:53]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ajwong@chromium.org/10735044/1

[commit-bot: I haz the power, 2012-07-11 05:23:27]

Failed to apply patch for base/json/json_string_value_serializer.h:
While running patch -p1 --forward --force;
patching file base/json/json_string_value_serializer.h
Hunk #1 FAILED at 4.
1 out of 1 hunk FAILED -- saving rejects to file
base/json/json_string_value_serializer.h.rej