[FastTextAutosizer] Inherit the text autosizing multiplier

Because font is inherited we had bugs due to the text autosizing
multiplier and the font getting out of sync. This patch changes
the text autosizing multiplier to inherit like the font properties.

TEST=display-type-change.html which failed before this patch.
BUG=378959

Review URL: https://codereview.chromium.org/319283002

git-svn-id: svn://svn.chromium.org/blink/trunk@175820 bbb929c8-8fbe-4397-9dbb-9b2b20218538