Use USE_GLIB flag instead of OS_XXXX for choosing whether to initialize glib.

BUG=170408

Review URL: https://codereview.chromium.org/176993003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252906 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252906