Move SkMatrixImageFilter.h into src/core.

Callers in Blink have been updated to call
SkImageFilter::CreateMatrixFilter() instead.

BUG=skia:3568

Review URL: https://codereview.chromium.org/1013753013

gyp/core.gypi

@@ -124,6 +124,7 @@
         '<(skia_src_path)/core/SkMath.cpp',
         '<(skia_src_path)/core/SkMatrix.cpp',
         '<(skia_src_path)/core/SkMatrixImageFilter.cpp',
+        '<(skia_src_path)/core/SkMatrixImageFilter.h',
         '<(skia_src_path)/core/SkMessageBus.h',
         '<(skia_src_path)/core/SkMetaData.cpp',
         '<(skia_src_path)/core/SkMipMap.cpp',
@@ -276,7 +277,6 @@
         '<(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',