SkValidatingReadBuffer: make sure we don't call readTypeface().

SkValidatingReadBuffer: make sure we don't call readTypeface().

Add an assert to make sure we're not calling this unimplemented method.

BUG=skia:3978
Committed: https://skia.googlesource.com/skia/+/a46ada5635351cf3ceefa1a3570212a21c2a8224

[mtklein_C, 2015-09-14 14:01:15]

The CQ bit was checked by mtklein@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-14 14:01:21]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1341753003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1341753003/1

[mtklein_C, 2015-09-14 14:03:48]

mtklein@chromium.org changed reviewers:
+ reed@google.com

[commit-bot: I haz the power, 2015-09-14 14:07:01]

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

[commit-bot: I haz the power, 2015-09-14 14:07:02]

Dry run: This issue passed the CQ dry run.

[reed1, 2015-09-14 17:48:46]

lgtm

[mtklein, 2015-09-14 18:08:52]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2015-09-14 18:09:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1341753003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1341753003/1

[commit-bot: I haz the power, 2015-09-14 18:09:45]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/a46ada5635351cf3ceefa1a3570212a21c2a8224