Some simple optimizations for improving GrAtlasTextContext perf

Some simple optimizations for improving GrAtlasTextContext perf

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/010db5346e425be8ce659b23b75943ee8ef9d537

[joshualitt, 2015-04-20 20:19:19]

joshualitt@google.com changed reviewers:
+ bsalomon@google.com, joshualitt@google.com

[joshualitt, 2015-04-20 20:19:19]

ptal

[bsalomon, 2015-04-21 12:36:25]

If these help, then lgtm.

[joshualitt, 2015-04-21 16:49:09]

The CQ bit was checked by joshualitt@google.com

[joshualitt, 2015-04-21 16:49:10]

The patchset sent to the CQ was uploaded after l-g-t-m from bsalomon@google.com
Link to the patchset: https://codereview.chromium.org/1093083003/#ps40001
(title: "simple optimizations")

[commit-bot: I haz the power, 2015-04-21 16:49:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1093083003/40001

[commit-bot: I haz the power, 2015-04-21 17:07:30]

Committed patchset #3 (id:40001) as
https://skia.googlesource.com/skia/+/010db5346e425be8ce659b23b75943ee8ef9d537