change all factories to return their base-class

include/effects/SkColorMatrixFilter.h

Index: include/effects/SkColorMatrixFilter.h
diff --git a/include/effects/SkColorMatrixFilter.h b/include/effects/SkColorMatrixFilter.h
index bd2b939a434f8abcb09cbe8064827bea5720d622..057e5cc3256a5bf72ecaf02e794e37fa48a6c962 100644
--- a/include/effects/SkColorMatrixFilter.h
+++ b/include/effects/SkColorMatrixFilter.h
@@ -13,10 +13,10 @@
 
 class SK_API SkColorMatrixFilter : public SkColorFilter {
 public:
-    static SkColorMatrixFilter* Create(const SkColorMatrix& cm) {
+    static SkColorFilter* Create(const SkColorMatrix& cm) {
         return new SkColorMatrixFilter(cm);
     }
-    static SkColorMatrixFilter* Create(const SkScalar array[20]) {
+    static SkColorFilter* Create(const SkScalar array[20]) {
         return new SkColorMatrixFilter(array);
     }