Optimize the blur convolution by only applying domain clamping where necessary. Split the blur con…

Optimize the blur convolution by only applying domain clamping where necessary.  Split the blur convolution into left and right margins which have clamping applied and a center portion which doesn't. Also reorder the convolve_gaussian() parameters to match GrConvolutionEffect params. Correctness is covered by existing tests; performance is covered by BlurImageFilter bench.

R=bsalomon@google.com

Committed: https://code.google.com/p/skia/source/detail?r=10444

[Stephen White, 2013-07-30 19:02:51]

Brian: PTAL. Thanks!

[bsalomon, 2013-07-30 20:53:43]

lgtm, but could you give the two convolve_gaussian functions different names?
Even something like convolve_gaussian_helper(). It seems like someone might read
this as recursive.

[Stephen White, 2013-07-30 21:04:54]

On 2013/07/30 20:53:43, bsalomon wrote:
> lgtm, but could you give the two convolve_gaussian functions different names?
> Even something like convolve_gaussian_helper(). It seems like someone might
read
> this as recursive.

Sure, will fix on landing.

[Stephen White, 2013-07-30 21:11:10]

Committed patchset #2 manually as r10444 (presubmit successful).