Introduce DEFINE_FONT_DATA_TYPE_CASTS, and use it

As a step to use toFoo, this cl introduces DEFINE_FONT_DATA_TYPE_CASTS, and use it.
In SegmentedFontData case, it already has own type cast macro. This cl removes it, and use
DEFINE_FONT_DATA_TYPE_CASTS.

BUG=309516

Review URL: https://codereview.chromium.org/401553002

git-svn-id: svn://svn.chromium.org/blink/trunk@178332 bbb929c8-8fbe-4397-9dbb-9b2b20218538