Implement getFamilyName for stream fonts on Linux.

Implement getFamilyName for stream fonts on Linux.

When SkFontMgr_fontconfig and SkFontMgr_FontConfigInterface create a
typeface from data they do not store the default font name and
getFamilyName will return the empty string. All of the code to handle
this properly now exists, it just needs to be hooked up.

BUG=skia:1508

Change-Id: I75f2a598a5451babb4a9ceb5e9a9e9d3daa41d60
Reviewed-on: https://skia-review.googlesource.com/7506
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Ben Wagner <bungeman@google.com>