SkDiscardablePixelRef objects are now marked immutable.

SkDiscardablePixelRef objects are now marked immutable.

I also specifically mentioned in the SkImageGenerator documentation
that it should always return the same information on subsequent calls
to getInfo() and getPixels().

Motivation: When a bitmap is recorded into a SkPicture, it will choose
whether to shallow- or deep-copy itself into the SkBitmapHeap based on
the immutable flag.  Failing to set it would make picture recording slow.

BUG=

Committed: http://code.google.com/p/skia/source/detail?r=12445

[reed1, 2013-12-02 18:36:36]

lgtm -- if we need to in the future, we could have a virtual on the generator
that make this a choice...

[reed1, 2013-12-02 18:37:26]

I take it back -- it should *always* be immutable

[scroggo, 2013-12-02 19:39:55]

On 2013/12/02 18:37:26, reed1 wrote:
> I take it back -- it should *always* be immutable

lgtm

[commit-bot: I haz the power, 2013-12-02 21:15:43]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/halcanary@google.com/99303003/1

[commit-bot: I haz the power, 2013-12-02 22:32:55]

Change committed as 12445