Remove some unnecessary uses of SkOnce.

Remove some unnecessary uses of SkOnce.

  - gm/imagefiltersgraph.cpp can just use a global registrar
  - SkScaledImageCache always accesses its global under a lock

BUG=skia:

Committed: http://code.google.com/p/skia/source/detail?r=14897

[bungeman-skia, 2014-05-27 16:21:21]

lgtm with comment nit

https://codereview.chromium.org/297273006/diff/1/src/core/SkScaledImageCache.cpp
File src/core/SkScaledImageCache.cpp (right):

https://codereview.chromium.org/297273006/diff/1/src/core/SkScaledImageCache....
src/core/SkScaledImageCache.cpp:676: // gMutex is always held when this is
called, so we don't need to be fancy in here.
We do have places where we have this requirement (that a mutex be held when
calling). It would be nice to put this in a comment on the method.

/** Must hold gMutex when calling. */

[mtklein, 2014-05-27 16:23:10]

https://codereview.chromium.org/297273006/diff/1/src/core/SkScaledImageCache.cpp
File src/core/SkScaledImageCache.cpp (right):

https://codereview.chromium.org/297273006/diff/1/src/core/SkScaledImageCache....
src/core/SkScaledImageCache.cpp:676: // gMutex is always held when this is
called, so we don't need to be fancy in here.
On 2014/05/27 16:21:21, bungeman1 wrote:
> We do have places where we have this requirement (that a mutex be held when
> calling). It would be nice to put this in a comment on the method.
> 
> /** Must hold gMutex when calling. */

Done.

[mtklein, 2014-05-27 16:23:15]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-05-27 16:23:28]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/mtklein@chromium.org/297273006/20001

[commit-bot: I haz the power, 2014-05-27 16:28:46]

Change committed as 14897