Fix texture allocation in SWMaskHelper

Fix texture allocation in SWMaskHelper

[robertphillips, 2013-07-19 17:36:04]

This patch removes the clear of the mask's texture since, due to its use, we
should never be sampling outside of the initialized are. This means that the
mask no longer has to be a rendertarget. One downside of this change is that we
aren't providing a hint to the driver that the texture's old contents are
discardable (not that the old code was really doing so either). 

The forthcoming changes to not reuse scratch textures on deferred architectures
should provide the driver with the needed hint that the mask doesn't need to be
ghosted.

[bsalomon, 2013-07-19 17:42:28]

https://codereview.chromium.org/19789006/diff/3001/src/gpu/GrSWMaskHelper.cpp
File src/gpu/GrSWMaskHelper.cpp (left):

https://codereview.chromium.org/19789006/diff/3001/src/gpu/GrSWMaskHelper.cpp...
src/gpu/GrSWMaskHelper.cpp:135: 
I think we want to delete from here...

https://codereview.chromium.org/19789006/diff/3001/src/gpu/GrSWMaskHelper.cpp...
src/gpu/GrSWMaskHelper.cpp:149: texture->writePixels(0, 0, fBM.width(),
fBM.height(),
... up to this line.

[robertphillips, 2013-07-19 17:54:47]

https://codereview.chromium.org/19789006/diff/3001/src/gpu/GrSWMaskHelper.cpp
File src/gpu/GrSWMaskHelper.cpp (left):

https://codereview.chromium.org/19789006/diff/3001/src/gpu/GrSWMaskHelper.cpp...
src/gpu/GrSWMaskHelper.cpp:149: texture->writePixels(0, 0, fBM.width(),
fBM.height(),
You are correct - done.

[bsalomon, 2013-07-19 18:07:49]

lgtm

[robertphillips, 2013-07-19 18:13:17]

committed as r10197