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

include/core/SkImageFilter.h

Index: include/core/SkImageFilter.h
diff --git a/include/core/SkImageFilter.h b/include/core/SkImageFilter.h
index b64a2957fdf993826acc863997a95811ebc8a611..40bd38a949130a0f780330d17bbd960897f426d2 100644
--- a/include/core/SkImageFilter.h
+++ b/include/core/SkImageFilter.h
@@ -8,6 +8,7 @@
 #ifndef SkImageFilter_DEFINED
 #define SkImageFilter_DEFINED
 
+#include "SkFilterQuality.h"
 #include "SkFlattenable.h"
 #include "SkMatrix.h"
 #include "SkRect.h"
@@ -192,6 +193,13 @@ public:
     // Default impl returns union of all input bounds.
     virtual void computeFastBounds(const SkRect&, SkRect*) const;
 
+    /**
+     * Create an SkMatrixImageFilter, which transforms its input by the given matrix.
+     */
+    static SkImageFilter* CreateMatrixFilter(const SkMatrix& matrix,
+                                             SkFilterQuality,
+                                             SkImageFilter* input = NULL);
+
 #if SK_SUPPORT_GPU
     /**
      * Wrap the given texture in a texture-backed SkBitmap.