Refactor FastTextAutosizer to remove the TextAutosizer dependencies

This patch copies TextAutosizer's functions into FastTextAutosizer.cpp
so that we can refactor this code for understandability. This is the
first patch of a few and just moves the code. A followup will actually
refactor the functions.

BUG=302005

Review URL: https://codereview.chromium.org/200603002

git-svn-id: svn://svn.chromium.org/blink/trunk@169387 bbb929c8-8fbe-4397-9dbb-9b2b20218538