Fix GetOSVersionName on Windows

os.uname is only available on unix platforms, while platform.uname should be available almost anywhere

BUG=225939
R=dtu@chromium.org, kbr@chromium.org

Review URL: https://codereview.chromium.org/26095002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227206 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227206