reduce alloc overhead for SkCanvas

reduce alloc overhead for SkCanvas

use pre-allocated space in the canvas to avoid initial calls to malloc

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/b679ca8926a832274b14fdb512f88f64b61d32ea

[reed2, 2015-04-07 03:33:17]

The CQ bit was checked by reed@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-04-07 03:33:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1060583007/1

[reed2, 2015-04-07 03:34:32]

reed@chromium.org changed reviewers:
+ mtklein@google.com, reed@android.com

[reed2, 2015-04-07 03:34:33]

just one more left to eliminate, the device itself

[commit-bot: I haz the power, 2015-04-07 03:39:35]

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

[commit-bot: I haz the power, 2015-04-07 03:39:35]

This issue passed the CQ dry run.

[mtklein, 2015-04-07 11:37:22]

Before:

 
26M	1	2.25µs	2.4µs	2.58µs	8.4µs	37%	█▂▁▁▁▁▁▂▂▁▁▁▁▂▁▁▁▁▁▁▁▁▂▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁	nonrendering	picture_overhead_draw
 
13M	23	1.19µs	1.38µs	1.31µs	1.66µs	8%	▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁	nonrendering	picture_overhead_nodraw

After:
 
26M	1	2.05µs	2.6µs	2.82µs	7.65µs	36%	▆▃▃▂▂▂▂▂▂▂▂▂▂█▂▁▁▁▁▂▂▁▂▂▁▁▂▁▁▂▁▁▂▁▁▂▂▂▁▂	nonrendering	picture_overhead_draw
 
13M	32	732ns	741ns	771ns	1.05µs	12%	▁▂▁██▁▁▁▁▂▁▁▁▁▁▁▁▁▁▁▁▁▁▁██▁▁▁▁▁▁▁▁▁▁▁▁▁▁	nonrendering	picture_overhead_nodraw

Nice!

[mtklein, 2015-04-07 11:38:32]

lgtm

[mtklein, 2015-04-07 11:40:37]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2015-04-07 11:40:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1060583007/1

[commit-bot: I haz the power, 2015-04-07 11:40:54]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/b679ca8926a832274b14fdb512f88f64b61d32ea