Add new bench for occluded blurmaskfilter draws

tools/sk_tool_utils.h

Index: tools/sk_tool_utils.h
diff --git a/tools/sk_tool_utils.h b/tools/sk_tool_utils.h
index c4d7c8a265b26c463a09df36aff5085386da9aab..c13d99f2d4c7dcbb9083c9a3877e05c60bfdd9cf 100644
--- a/tools/sk_tool_utils.h
+++ b/tools/sk_tool_utils.h
@@ -20,6 +20,7 @@ class SkBitmap;
 class SkCanvas;
 class SkPaint;
 class SkPath;
+class SkRRect;
 class SkShader;
 class SkTestFont;
 class SkTextBlobBuilder;
@@ -130,6 +131,8 @@ namespace sk_tool_utils {
     // so it is slow!
     SkBitmap slow_blur(const SkBitmap& src, float sigma);
 
+    SkRect compute_central_occluder(const SkRRect& rr);
+
     // A helper object to test the topological sorting code (TopoSortBench.cpp & TopoSortTest.cpp)
     class TopoTestNode {
     public: