Fix for crash on large image blur sigma values.

This was crashing on the GPU path, due to a failed texture allocation.
The belt-and-suspenders fix is to:

1) Limit the GPU path to only allocate up to maxTextureSize.
2) Limit both the raster and GPU paths to reasonable blur sizes (box blur
   kernel size of 1000, resulting in a sigma limit of 532).

R=bsalomon@google.com
BUG=skia:

Review URL: https://codereview.chromium.org/209353014

git-svn-id: http://skia.googlecode.com/svn/trunk@13923 2bbb7eff-a529-9590-31e7-b0007b416f81
3 files changed