[Mac] In PlatformThread::CurrentId(), use pthread_self() instead of mach_thread_self().

BUG=105513
TEST=none


Review URL: http://codereview.chromium.org/9281011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@118780 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed