change all factories to return their base-class

will watch DEPS roll to see if there are chrome sites needing updates

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1535353002

TBR=

Review URL: https://codereview.chromium.org/1535353002
diff --git a/bench/MatrixConvolutionBench.cpp b/bench/MatrixConvolutionBench.cpp
index 6302f12..05f0193 100644
--- a/bench/MatrixConvolutionBench.cpp
+++ b/bench/MatrixConvolutionBench.cpp
@@ -50,7 +50,7 @@
 
 private:
     typedef Benchmark INHERITED;
-    SkMatrixConvolutionImageFilter* fFilter;
+    SkImageFilter* fFilter;
     SkString fName;
 };