Added Doc for GetAllocator in SkResourceCache and SkBitmapCache

Added Doc for GetAllocator in SkResourceCache and SkBitmapCache

BUG=skia:2896
Committed: https://skia.googlesource.com/skia/+/8159146699f691b88f60564fc0811a6da3e8693f

[Rémi Piotaix, 2014-09-02 18:05:51]

piotaixr@chromium.org changed reviewers:
+ junov@chromium.org, reed@google.com

[reed1, 2014-09-02 18:08:53]

I like the comment additions.

Was there a call-site we needed to update, that was crashing on NULL?

[reed1, 2014-09-02 18:16:03]

The bug now is updated to make it clear that more Documentation was needed.

lgtm

[Rémi Piotaix, 2014-09-02 18:19:56]

The CQ bit was checked by piotaixr@chromium.org

[commit-bot: I haz the power, 2014-09-02 18:20:29]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/piotaixr@chromium.org/533713003/40001

[commit-bot: I haz the power, 2014-09-02 18:27:16]

Committed patchset #3 (id:40001) as 8159146699f691b88f60564fc0811a6da3e8693f

[Justin Novosad, 2014-09-02 18:39:09]

On 2014/09/02 18:08:53, reed1 wrote:
> I like the comment additions.
> 
> Was there a call-site we needed to update, that was crashing on NULL?

I think the only such call site is in a not yet submitted CL.