[CSS Font Loading] Remove FontFace#ready, fold its functionality into FontFace#load

[CSS Font Loading] Remove FontFace#ready, fold its functionality into FontFace#load

As per a discussion on www-style [1], FontFace#ready is removed from the
spec [2], and FontFace#load() is changed to return a Promise which
fulfills when the font is ready.

[1] http://lists.w3.org/Archives/Public/www-style/2014Mar/0069.html
[2] http://dev.w3.org/csswg/css-font-loading/

TEST=fast/css/fontface-methods.html
BUG=53213
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=169507

[dglazkov, 2014-03-06 18:41:39]

lgtm.

[Kunihiko Sakamoto, 2014-03-07 00:55:53]

The CQ bit was checked by ksakamoto@chromium.org

[commit-bot: I haz the power, 2014-03-07 00:56:03]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ksakamoto@chromium.org/184633005/1

[Kunihiko Sakamoto, 2014-03-07 01:20:59]

The CQ bit was unchecked by ksakamoto@chromium.org

[Kunihiko Sakamoto, 2014-03-07 10:27:58]

I would like to wait for the discussion thread in www-style to settle down.

[Kunihiko Sakamoto, 2014-03-18 10:58:17]

The CQ bit was checked by ksakamoto@chromium.org

[commit-bot: I haz the power, 2014-03-18 10:58:27]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ksakamoto@chromium.org/184633005/20001

[commit-bot: I haz the power, 2014-03-18 11:05:09]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-03-18 11:05:10]

Try jobs failed on following builders:
  tryserver.blink on mac_blink_rel

[Kunihiko Sakamoto, 2014-03-19 01:06:26]

The CQ bit was checked by ksakamoto@chromium.org

[commit-bot: I haz the power, 2014-03-19 01:06:35]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ksakamoto@chromium.org/184633005/20001

[commit-bot: I haz the power, 2014-03-19 02:44:57]

Change committed as 169507