gn format: support absolute file system paths

gn format: support absolute file system paths

And update help text.

R=brettw@chromium.org
BUG=348474
Committed: https://crrev.com/ee0152bda8e2a11b83f996df3f0601fe4187eab5
Cr-Commit-Position: refs/heads/master@{#297926}

[scottmg, 2014-10-02 21:54:29]

https://codereview.chromium.org/613083003/diff/20001/tools/gn/command_format.cc
File tools/gn/command_format.cc (right):

https://codereview.chromium.org/613083003/diff/20001/tools/gn/command_format....
tools/gn/command_format.cc:555: CHECK(!in_place) << "TODO(scottmg)";
(is there an easy way to map a SourceFile back to disk file?)

[brettw, 2014-10-02 22:03:27]

lgtm

https://codereview.chromium.org/613083003/diff/20001/tools/gn/command_format.cc
File tools/gn/command_format.cc (right):

https://codereview.chromium.org/613083003/diff/20001/tools/gn/command_format....
tools/gn/command_format.cc:555: CHECK(!in_place) << "TODO(scottmg)";
On 2014/10/02 21:54:29, scottmg wrote:
> (is there an easy way to map a SourceFile back to disk file?)

setup.build_settings()->GetFullPath(source_file)

[scottmg, 2014-10-02 22:04:33]

The CQ bit was checked by scottmg@chromium.org

[commit-bot: I haz the power, 2014-10-02 22:05:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/613083003/20001

[commit-bot: I haz the power, 2014-10-02 22:32:03]

Committed patchset #2 (id:20001) as 71fba890ec3a6125a72305ce078ba0cafac73d65

[commit-bot: I haz the power, 2014-10-02 22:32:33]

Patchset 2 (id:??) landed as
https://crrev.com/ee0152bda8e2a11b83f996df3f0601fe4187eab5
Cr-Commit-Position: refs/heads/master@{#297926}