Acquire lock in Args::SetSystemVars()

Acquire lock in Args::SetSystemVars()

Since the function manipulates Args::declared_arguments_, it needs to
hold the lock to avoid heap corruption.

BUG=335587
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=247710

[Jens Widell, 2014-01-29 14:03:28]

Uploading trivial fix based on halyavin's comment in crbug.com/335587.  Matches
the crashes I've reproduced, and seems to have fixed the bug.  (The crash is
somewhat elusive.)

[brettw, 2014-01-29 14:11:15]

Sweet! LGTM

[Jens Widell, 2014-01-29 14:20:42]

On 2014/01/29 14:11:15, brettw wrote:
> Sweet! LGTM

Thanks.

How does one commit a GN fix?  Do I just check the 'commit' checkbox, and then
the rest happens by magic?  :-)

[commit-bot: I haz the power, 2014-01-29 14:23:17]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jl@opera.com/136783005/1

[halyavin, 2014-01-29 14:25:26]

On 2014/01/29 14:20:42, Jens Lindström wrote:
> On 2014/01/29 14:11:15, brettw wrote:
> > Sweet! LGTM
> 
> Thanks.
> 
> How does one commit a GN fix?  Do I just check the 'commit' checkbox, and then
> the rest happens by magic?  :-)

Yes, unless it doesn't. In this case one need to check the 'commit' checkbox
again.

[Jens Widell, 2014-01-29 14:28:55]

On 2014/01/29 14:25:26, halyavin wrote:
> On 2014/01/29 14:20:42, Jens Lindström wrote:
> > the rest happens by magic?  :-)
> 
> Yes, unless it doesn't. In this case one need to check the 'commit' checkbox
> again.

I was thinking more about the downloaded GN binaries.  Are they rebuilt
automatically when a GN fix lands, or does someone need to do that manually and
then update the *.sha1 files in tools/gn/bin/*/?

[commit-bot: I haz the power, 2014-01-29 17:08:05]

Change committed as 247710

[brettw, 2014-01-30 00:26:05]

On 2014/01/29 17:08:05, I haz the power (commit-bot) wrote:
> Change committed as 247710

I need to push new binaries. Unfortunately, I probably won't be able to do this 
until early next week.