Do not use SkCreateTypefaceFromCTFont for custom fonts

SkCreateTypefaceFromCTFont implies fonts are non-local
(i.e. serialized as font name only, not the glyphs). This
does not work with the dynamically loaded fonts, so just
keep the SkTypeface we used to create in FontCustomPlatformDataMac
rather than create one from CTFont.

BUG=426088

Review URL: https://codereview.chromium.org/691733004

git-svn-id: svn://svn.chromium.org/blink/trunk@184884 bbb929c8-8fbe-4397-9dbb-9b2b20218538