Change the default SOCKS version used by gnome settings (and environment...

Change the default SOCKS version used by gnome settings (and environment variables) to be 5 instead of 4.

BUG=56833
TEST=Open Chrome in gnome. Go to change the proxy settings (which will pop open the gnome network settings). Enter as socks proxy server, "localhost:8080". Now load chrome://net-internals/#proxy and verify that it says the proxy server is "socks5://localhost:8080" (and NOT socks4://localhost:8080).
Review URL: http://codereview.chromium.org/3413037

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@60734 0039d316-1c4b-4281-b951-d872f2087c98