content/aura: Use gfx::Canvas::DrawRect instead of unwrapping SkCanvas.

content/aura: Use gfx::Canvas::DrawRect instead of unwrapping SkCanvas.

There's no need to go through gfx::Canvas to the SkCanvas underneath,
use the gfx::Canvas API instead.

R=sadrul
BUG=466426
Committed: https://crrev.com/5cfc9f5a1f67bfd94e96e77a3b6e7aa7b1c3fcee
Cr-Commit-Position: refs/heads/master@{#324255}

[danakj, 2015-04-07 21:21:20]

Depends on https://codereview.chromium.org/1066183002/

[sadrul, 2015-04-08 15:53:22]

lgtm

[danakj, 2015-04-08 16:29:51]

The CQ bit was checked by danakj@chromium.org

[commit-bot: I haz the power, 2015-04-08 16:30:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1064183002/1

[commit-bot: I haz the power, 2015-04-08 18:34:10]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-08 18:36:07]

Patchset 1 (id:??) landed as
https://crrev.com/5cfc9f5a1f67bfd94e96e77a3b6e7aa7b1c3fcee
Cr-Commit-Position: refs/heads/master@{#324255}