linux_aura: Use the system font rendering settings.

We now read the system font, antialiasing, subpixel rendering
and hinting properties from XSettings.

Note that we don't use the hinting flag yet; I don't see it
used in render_text_pango.cc or anywhere else in the text
stack. Notably, we also only use subpixel rendering as a boolean.

BUG=318395, 318464

Review URL: https://codereview.chromium.org/116573006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241704 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241704