Rename 'webkit' target to 'blink_web'.

BUG=None
TEST=None
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/150243003

git-svn-id: svn://svn.chromium.org/blink/trunk@166769 bbb929c8-8fbe-4397-9dbb-9b2b20218538