Remove zoom argument from size-setting FontBuilder functions.

This information is superflous at the time of applying properties,
since we have update the computed size at the time of
constructing the Font instance, which is is what we should do.

This enables the path toward making most font-related property
application be code-generated.

R=ksakamoto@chromium.org,eae
BUG=

Review URL: https://codereview.chromium.org/200573006

git-svn-id: svn://svn.chromium.org/blink/trunk@169285 bbb929c8-8fbe-4397-9dbb-9b2b20218538