NSS: don't set environment variables when multi-threaded.

NSS: don't set environment variables when multi-threaded.

We can't alter the envionment once we have gone multithreaded because
glibc's getenv doesn't take the environment lock. Thus we add an
EarlyNSSInit() function which can do so, early in startup.

BUG=66835
TEST=ThreadSanitizer

[wtc, 2011-01-13 00:07:02]

LGTM.  I suggested some changes below.

http://codereview.chromium.org/6185005/diff/1/base/nss_util.cc
File base/nss_util.cc (right):

http://codereview.chromium.org/6185005/diff/1/base/nss_util.cc#newcode330
base/nss_util.cc:330: #if defined(OS_LINUX)
This ifdef should be
    #if defined(USE_NSS)
to match the ifdef at lines 215-227.

http://codereview.chromium.org/6185005/diff/1/base/nss_util.h
File base/nss_util.h (right):

http://codereview.chromium.org/6185005/diff/1/base/nss_util.h#newcode25
base/nss_util.h:25: void EarlyNSSInit();
The comment should point out that this function doesn't initialize NSS.

Please rename this function EarlySetupForNSSInit (or something along that line).

http://codereview.chromium.org/6185005/diff/1/chrome/app/chrome_main.cc
File chrome/app/chrome_main.cc (right):

http://codereview.chromium.org/6185005/diff/1/chrome/app/chrome_main.cc#newco...
chrome/app/chrome_main.cc:718: base::EarlyNSSInit();
Nit: since EarlyNSSInit doesn't use the Chrome path provider, it seems
that we can call EarlyNSSInit earlier, immediately after the SecupCRT call
at line 712.

At least, we should not call EarlyNSSInit in the middle of the code block
that sets up the Chrome path provider (lines 714-724).