Fix SkOffsetImageFilter to use a temporary for bounds computations.

SkOffsetImageFilter::onFilterBounds() was writing to *dst, and later
referring to src. These may be the same memory location, so the results
were incorrect.

Covered by the 5th test case in offsetimagefilter.

BUG=skia:

Review URL: https://codereview.chromium.org/195163004

git-svn-id: http://skia.googlecode.com/svn/trunk@13744 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed