Pour FontFastPath.cpp back into Font.cpp.

There is no longer a need to split these functions into a separate class.

R=eae,eseidel,ksakamoto@chromium.org
BUG=319475

Review URL: https://codereview.chromium.org/137803019

git-svn-id: svn://svn.chromium.org/blink/trunk@167036 bbb929c8-8fbe-4397-9dbb-9b2b20218538