Move to SkStreamAsset for SkTypeface streams.

Move to SkStreamAsset for SkTypeface streams.

SkTypeface is moving to use SkStreamAsset instead of SkStream. The
implementations are already assuming this, and all users are in
practice already creating the correct types. This change simply
clarifies existing practice and documents actual restrictions.

The Skia side change will be https://codereview.chromium.org/869763002/

Committed: https://crrev.com/9be085c313537c895fcaf1b8ec2ab33593743fee
Cr-Commit-Position: refs/heads/master@{#313196}

[bungeman-chromium, 2015-01-26 17:15:30]

bungeman@chromium.org changed reviewers:
+ jam@chromium.org, jln@chromium.org

[bungeman-chromium, 2015-01-26 17:15:31]

This doesn't change any behavior or bits, it just clarifies the actual type
being used.

[jam, 2015-01-26 22:17:43]

lgtm

[bungeman-chromium, 2015-01-27 00:51:40]

The CQ bit was checked by bungeman@chromium.org

[commit-bot: I haz the power, 2015-01-27 00:53:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/870133002/40001

[commit-bot: I haz the power, 2015-01-27 01:41:29]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-01-27 01:42:48]

Patchset 3 (id:??) landed as
https://crrev.com/9be085c313537c895fcaf1b8ec2ab33593743fee
Cr-Commit-Position: refs/heads/master@{#313196}