Add cmap 3,0 (symbol) as Unicode fallback.

Add cmap 3,0 (symbol) as Unicode fallback.

FreeType automatically selects the 'most Unicode' cmap available,
otherwise the default cmap is NULL. When this happens the fallback
should include the 3,0 symbol cmap, as is outlined in the Apple
TrueType documentation. This cmap should effectively be a Unicode
mapping, but exclusively in the private use area.

BUG=skia:1873, chromium:489452
Committed: https://skia.googlesource.com/skia/+/726cf9038aae3f4dffc79a97645388f32224b22d

[bungeman-skia, 2015-06-05 19:53:17]

The CQ bit was checked by bungeman@google.com to run a CQ dry run

[commit-bot: I haz the power, 2015-06-05 19:53:51]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1163833003/1

[commit-bot: I haz the power, 2015-06-05 19:59:59]

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

[commit-bot: I haz the power, 2015-06-05 20:00:00]

Dry run: This issue passed the CQ dry run.

[bungeman-skia, 2015-06-05 20:27:34]

bungeman@google.com changed reviewers:
+ reed@google.com

[reed1, 2015-06-05 20:35:17]

lgtm

[bungeman-skia, 2015-06-05 20:36:58]

The CQ bit was checked by bungeman@google.com

[commit-bot: I haz the power, 2015-06-05 20:37:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1163833003/1

[commit-bot: I haz the power, 2015-06-05 20:38:16]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/726cf9038aae3f4dffc79a97645388f32224b22d