Fix include paths to resources in blink_resources.grd

Otherwise this will break Chromium when Blink is rolled there, as it happened
in https://codereview.chromium.org/19537010/

R=abarth@chromium.org
BUG=

Review URL: https://codereview.chromium.org/19874004

git-svn-id: svn://svn.chromium.org/blink/trunk@154795 bbb929c8-8fbe-4397-9dbb-9b2b20218538