Reland "Extend WidthCache to include glyph overflow bounds"

Extend the font WidthCache to always compute and cache the glyph bounding box,
regardless of whether the glyphOverflow parameter is supplied. This ensures that
subsequent calls can always be served from the cache and as such the cache can
now also be used for text measurements where the bounding box of the glyphs is
required. 

BUG=347186
R=dominik.rottsches@intel.com

Originally landed as r174230 and reverted as r174318 due to snowleopard debug
test failures.

Review URL: https://codereview.chromium.org/295853002

git-svn-id: svn://svn.chromium.org/blink/trunk@174917 bbb929c8-8fbe-4397-9dbb-9b2b20218538