Use highp for distance field texture coord varyings.

Use highp for distance field texture coord varyings.

Because the glyph texture atlas is 1024x2048, on certain platforms
using mediump UVs is not enough resolution for doing texture lookups
and getting good results for distance fields. Bumping these
to highp solves this problem.

BUG=skia:3445
Committed: https://skia.googlesource.com/skia/+/9671ecd44e48e8bbe1361830717b79c9c4dc9d17

[jvanverth1, 2015-02-23 20:33:48]

jvanverth@google.com changed reviewers:
+ bsalomon@google.com

[jvanverth1, 2015-02-23 20:39:36]

Forgot to update this for the other distance field shaders -- can hold off on
the review for the moment.

[jvanverth1, 2015-02-23 20:53:37]

On 2015/02/23 20:39:36, jvanverth1 wrote:
> Forgot to update this for the other distance field shaders -- can hold off on
> the review for the moment.

Ok, done and tested.

[bsalomon, 2015-02-23 20:55:53]

lgtm

[jvanverth1, 2015-02-23 21:01:14]

The CQ bit was checked by jvanverth@google.com

[commit-bot: I haz the power, 2015-02-23 21:01:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/951003002/20001

[commit-bot: I haz the power, 2015-02-23 21:08:43]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/9671ecd44e48e8bbe1361830717b79c9c4dc9d17