Move implementation of SkFilterShader into its source file.

Since SkFilterShader has its own header file, makes more sense to have a
separate source file to implement it rather than placing it in a "random"
SkColorFilter.cpp file.

R=robertphillips@google.com

Review URL: https://codereview.chromium.org/19305004

git-svn-id: http://skia.googlecode.com/svn/trunk@10101 2bbb7eff-a529-9590-31e7-b0007b416f81
3 files changed