Mac: More pluming for OOP font loading

* Add font_descriptor and corresponding pluming to send an NSFont over IPC.

* Rejigger font_loader to accept an NSFont as input and output an ATSFontContainerRef.  The reasoning behind this is that WebKit ultimately controls the font lifetime and we can only deactivate the font container once the font is no longer in use.

BUG=29729
Test=Unit tests should pass.

Review URL: http://codereview.chromium.org/2804001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@50076 0039d316-1c4b-4281-b951-d872f2087c98
11 files changed