Implement crop rect for lighting image filters. Changes for the CPU path were fairly...

Implement crop rect for lighting image filters. Changes for the CPU path were fairly straightforward: use the bounds rectangle when traversing the pixels, not the source rectangle.

For the GPU path, this required modifying the signature of SkImageFilter::asNewEffect() to receive the bounds offset, so that the lighting filters could offset the light position by the offset. It also required modifying the base-class implementation of SkImageFilter::filterImageGPU() (which implements single-pass filters) to intersect against the bounds rect, to pass its offset to asNewEffect(), and to modify the caller's offset (so it's drawn in the correct place).

Note: this will require rebaselining the lighting GM. Six new test cases were added, to accommodate a cropped version of each lighting filter.

R=bsalomon@google.com, reed@google.com

Review URL: https://codereview.chromium.org/20426002

git-svn-id: http://skia.googlecode.com/svn/trunk@10379 2bbb7eff-a529-9590-31e7-b0007b416f81