Do some minor pre cleanup work before converting all xfermodes to XPs.

Do some minor pre cleanup work before converting all xfermodes to XPs.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/38cd055215acbeb8671e6bf5dcbfc926bd9e98cd

[egdaniel, 2015-01-14 15:07:01]

egdaniel@google.com changed reviewers:
+ bsalomon@google.com

[egdaniel, 2015-01-14 15:07:02]

Nothing big here, just minor changes before all my xfer changes.

[bsalomon, 2015-01-14 15:18:13]

lgtm, comments about comments.

https://codereview.chromium.org/853543003/diff/1/include/core/SkXfermode.h
File include/core/SkXfermode.h (right):

https://codereview.chromium.org/853543003/diff/1/include/core/SkXfermode.h#ne...
include/core/SkXfermode.h:193: /** A subclass may implement this factory
function to work with the GPU backend. It is legal
Let's clean this up a bit.

"Implemented by a subclass to support use as an image filter in the GPU backend.
When used as an image filter the xfer mode blends the source color against a
background texture rather than the destination. It is implemented as a fragment
processor. This can be called with both params set to NULL to query whether it
would succeed. Otherwise, both params are required. Upon success the function
returns true and the caller owns a ref to the fragment parameter. Upon failure
false is returned and the processor param is not written to."

https://codereview.chromium.org/853543003/diff/1/src/effects/SkXfermodeImageF...
File src/effects/SkXfermodeImageFilter.cpp (right):

https://codereview.chromium.org/853543003/diff/1/src/effects/SkXfermodeImageF...
src/effects/SkXfermodeImageFilter.cpp:115: // This is checked with the
background texture as NULL here since we have no actual texture,
Does this comment add much? Maybe just "Call asFragmentProcessor() with NULLs to
use it as a query without creating a processor."

[egdaniel, 2015-01-14 15:54:30]

The CQ bit was checked by egdaniel@google.com

[commit-bot: I haz the power, 2015-01-14 15:55:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/853543003/20001

[commit-bot: I haz the power, 2015-01-14 16:05:14]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/38cd055215acbeb8671e6bf5dcbfc926bd9e98cd