Implement font-family: initial.

Implement font-family: initial.

It appears that this never worked correctly. To implement,
I extracted the code we use to set initial value for document and
started using it when applying initial font-family value.

BUG=354110
R=eseidel,eae

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=169592

[eae, 2014-03-19 21:55:42]

LGTM

[eae, 2014-03-19 21:55:46]

The CQ bit was checked by eae@chromium.org

[commit-bot: I haz the power, 2014-03-19 21:55:57]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dglazkov@chromium.org/197213034/20001

[commit-bot: I haz the power, 2014-03-19 22:21:26]

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

[commit-bot: I haz the power, 2014-03-19 22:21:27]

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

[dglazkov, 2014-03-19 22:35:20]

The CQ bit was checked by dglazkov@chromium.org

[commit-bot: I haz the power, 2014-03-19 22:35:50]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dglazkov@chromium.org/197213034/20001

[commit-bot: I haz the power, 2014-03-19 23:39:13]

Change committed as 169592