Printing: Push checking of |context| one level lower, as the different

platforms have different expectations at this level.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/3418034

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@60728 0039d316-1c4b-4281-b951-d872f2087c98