Move SkMatrixImageFilter into core, and add a factory fn for it.

BUG=skia:

Review URL: https://codereview.chromium.org/1011273003
diff --git a/gyp/core.gypi b/gyp/core.gypi
index 2e9fb1b..f02c585 100644
--- a/gyp/core.gypi
+++ b/gyp/core.gypi
@@ -123,6 +123,7 @@
         '<(skia_src_path)/core/SkMaskGamma.h',
         '<(skia_src_path)/core/SkMath.cpp',
         '<(skia_src_path)/core/SkMatrix.cpp',
+        '<(skia_src_path)/core/SkMatrixImageFilter.cpp',
         '<(skia_src_path)/core/SkMessageBus.h',
         '<(skia_src_path)/core/SkMetaData.cpp',
         '<(skia_src_path)/core/SkMipMap.cpp',
@@ -275,6 +276,7 @@
         '<(skia_include_path)/core/SkMaskFilter.h',
         '<(skia_include_path)/core/SkMath.h',
         '<(skia_include_path)/core/SkMatrix.h',
+        '<(skia_include_path)/core/SkMatrixImageFilter.h',
         '<(skia_include_path)/core/SkMetaData.h',
         '<(skia_include_path)/core/SkMultiPictureDraw.h',
         '<(skia_include_path)/core/SkOnce.h',