Fix artifacts in distance field rendering due to bilerp

Fix artifacts in distance field rendering due to bilerp

Because we were using the full distance field glyph rect, there were cases
when a neighboring texel might be set to full value (e.g. we might copy the
glyph over old data after a purge). This was giving artifacts, and insetting
the rect by 1 solves the problem. In doing this, I discovered that removing the
extra 1 texel pad around the glyph meant to handle bilerp, and insetting by 2,
works just as well and saves space in the glyph atlas.

Committed: http://code.google.com/p/skia/source/detail?r=14203

[bsalomon, 2014-04-15 16:10:43]

The CQ bit was checked by bsalomon@google.com

[bsalomon, 2014-04-15 16:10:49]

On 2014/04/15 15:44:20, JimVV wrote:

lgtm

[commit-bot: I haz the power, 2014-04-15 16:10:55]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/jvanverth@google.com/239333002/1

[commit-bot: I haz the power, 2014-04-15 16:10:55]

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

[commit-bot: I haz the power, 2014-04-15 16:10:56]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a lowly provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[bsalomon, 2014-04-15 16:11:02]

The CQ bit was checked by bsalomon@google.com

[commit-bot: I haz the power, 2014-04-15 16:11:22]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/jvanverth@google.com/239333002/1

[commit-bot: I haz the power, 2014-04-15 17:53:25]

Change committed as 14203