ash: Use PaintRecorder in CursorWindowDelegate

ash: Use PaintRecorder in CursorWindowDelegate

Instead of accessing canvas() on the PaintContext directly, go
through the PaintRecorder. This will enable us to stop backing
the PaintContext with a Canvas for slimming-paint.

R=oshima
BUG=466426
Committed: https://crrev.com/2c03b15eace1106274f6aa78b87bb1d2e45b1864
Cr-Commit-Position: refs/heads/master@{#323959}

[danakj, 2015-04-03 17:30:26]

This replaces https://codereview.chromium.org/1021823002/, but depends on
https://codereview.chromium.org/1053143002/

[oshima, 2015-04-03 17:44:42]

lgtm

[danakj, 2015-04-04 01:25:47]

The CQ bit was checked by danakj@chromium.org

[commit-bot: I haz the power, 2015-04-04 01:26:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1056143002/1

[commit-bot: I haz the power, 2015-04-04 02:07:36]

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

[commit-bot: I haz the power, 2015-04-04 02:07:38]

Try jobs failed on following builders:
  linux_chromium_gn_chromeos_rel on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[danakj, 2015-04-06 21:16:25]

The CQ bit was checked by danakj@chromium.org

[commit-bot: I haz the power, 2015-04-06 21:16:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1056143002/1

[commit-bot: I haz the power, 2015-04-06 22:06:05]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-06 22:07:00]

Patchset 1 (id:??) landed as
https://crrev.com/2c03b15eace1106274f6aa78b87bb1d2e45b1864
Cr-Commit-Position: refs/heads/master@{#323959}