Maximize RLIMIT_AS resource limit in nacl_helper child before exec

NaCl processes need an unusually large amount of address space, because
they do huge PROT_NONE mappings to reserve contiguous regions much larger
than the memory that will actually be used.  An ambient RLIMIT_AS setting
can break this, so we need to raise the soft limit to the hard limit (which
is usually unlimited).

We cannot rely on doing this inside the nacl_helper child itself, so we
must do it in the zygote before it exec's nacl_helper_bootstrap.  That exec
itself could fail if the limit is too small, because nacl_helper_bootstrap
uses ELF program headers to reserve a large region of address space.

BUG= http://code.google.com/p/nativeclient/issues/detail?id=2438
TEST= nacl apps work when "ulimit -S -v 5376320" was run before starting chrome

R=mark@chromium.org,bsy@google.com,bradchen@google.com

Review URL: http://codereview.chromium.org/8528041

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@110123 0039d316-1c4b-4281-b951-d872f2087c98

• base/process_util.h[diff]
• base/process_util_posix.cc[diff]
• chrome/app/nacl_fork_delegate_linux.cc[diff]