Print with the correct physical dimensions when specified

If you specify a div in cm, mm or a similar unit of physical measurement and
print it you don't get an element of the expected size on paper. This is due
to the scaling factor we use when resizing the page for printing.

The scaling factor of 1.25 was introduced by https://trac.webkit.org/changeset/22945
and adopted in the Gtk port by http://wkbug.com/15576. It seems to
be a magic number that was 'about right'. From trial and error 1.33 seems to be
the magic number that produces output with the correct physical size.

I don't know how to test this.

BUG=273306

Review URL: https://codereview.chromium.org/1817873002

Cr-Commit-Position: refs/heads/master@{#383925}
29 files changed