Correctly declare skiagm::DCShader to be not flattenable.

Correctly declare skiagm::DCShader to be not flattenable.

Motivation: As part of my testing I serialize all of our GMs to SKP
files.  This was breaking my code.

Committed: https://skia.googlesource.com/skia/+/50b9307e96064637b10b6f070a807e320c45a005

[hal.canary, 2015-01-05 15:32:47]

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

[hal.canary, 2015-01-05 15:32:48]

PTAL at this tiny change.

[reed1, 2015-01-05 16:27:59]

lgtm w/ request for comment

https://codereview.chromium.org/832393002/diff/1/gm/dcshader.cpp
File gm/dcshader.cpp (right):

https://codereview.chromium.org/832393002/diff/1/gm/dcshader.cpp#newcode27
gm/dcshader.cpp:27: 
// We're not flattenable because ...

[hal.canary, 2015-01-05 16:37:25]

https://codereview.chromium.org/832393002/diff/1/gm/dcshader.cpp
File gm/dcshader.cpp (right):

https://codereview.chromium.org/832393002/diff/1/gm/dcshader.cpp#newcode27
gm/dcshader.cpp:27: 
On 2015/01/05 16:27:59, reed1 wrote:
> // We're not flattenable because ...

I don't care about serializing custom shaders, since the deserialization process
would also need to link in this class (In my PDF backend test code, I don't link
in the GMs; see http://crrev.com/832403002 ).

[hal.canary, 2015-01-05 16:44:34]

The CQ bit was checked by halcanary@google.com

[commit-bot: I haz the power, 2015-01-05 16:45:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/832393002/20001

[commit-bot: I haz the power, 2015-01-05 16:55:36]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/50b9307e96064637b10b6f070a807e320c45a005