Skip downloading of nacl toolchain for android. 
Nacl is not enabled in android and it takes too long to download the toolchain.

BUG=329646

Review URL: https://codereview.chromium.org/116833006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242405 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242405