Add SK_SUPPORT_LEGACY_PORTER_DUFF macro.

Add SK_SUPPORT_LEGACY_PORTER_DUFF macro.

This trick will be used to remove deprecated SkPorterDuff API. But first
we need to add it so Android can be updated later.

BUG=skia:3178
R=scroggo@google.com

Committed: https://skia.googlesource.com/skia/+/9ed02e40d1069a99c89013b2d442d20e07913206

[tfarina, 2014-12-03 01:35:13]

Leon, is it something like this?

ptal

[scroggo, 2014-12-03 01:43:10]

lgtm. You'll need derek or mike's approval since you're changing a header file.

[reed1, 2014-12-03 13:41:11]

reed@google.com changed reviewers:
+ reed@google.com

[reed1, 2014-12-03 13:41:12]

lgtm w/ request for comment

https://codereview.chromium.org/758133004/diff/1/include/effects/SkPorterDuff.h
File include/effects/SkPorterDuff.h (right):

https://codereview.chromium.org/758133004/diff/1/include/effects/SkPorterDuff...
include/effects/SkPorterDuff.h:15: 
// Temporary guard until we can remove the dependencies in android. Then we plan
to remove this entirely.

[tfarina, 2014-12-03 21:02:29]

https://codereview.chromium.org/758133004/diff/1/include/effects/SkPorterDuff.h
File include/effects/SkPorterDuff.h (right):

https://codereview.chromium.org/758133004/diff/1/include/effects/SkPorterDuff...
include/effects/SkPorterDuff.h:15: 
On 2014/12/03 13:41:11, reed1 wrote:
> // Temporary guard until we can remove the dependencies in android. Then we
plan
> to remove this entirely.

Done.

[tfarina, 2014-12-03 21:02:33]

The CQ bit was checked by tfarina@chromium.org

[commit-bot: I haz the power, 2014-12-03 21:03:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/758133004/20001

[commit-bot: I haz the power, 2014-12-03 21:13:08]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/9ed02e40d1069a99c89013b2d442d20e07913206