[Font Load Events] Kick off pending font loads in load()

CSSFontFace::load() only schedules font load, and actual fetch occurs
when the FontLoader timer fires, or loadPendingFonts() is called. This
patch adds call to loadPendingFonts() at the end of FontFaceSet::load()
and FontFace::load() methods, so font loads starts sooner.

BUG=53213

Review URL: https://codereview.chromium.org/157183002

git-svn-id: svn://svn.chromium.org/blink/trunk@166686 bbb929c8-8fbe-4397-9dbb-9b2b20218538