Add imgblur tool to assist BlurMaskFilter debugging

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 e0ad1df3ecca7a7a38b0b57fc1a2c87d45a03e13..052bade6a7b78704ee54fff102bb3529d63cd6e3 100644
--- a/tools/sk_tool_utils.h
+++ b/tools/sk_tool_utils.h
@@ -135,6 +135,11 @@ namespace sk_tool_utils {
     void create_tetra_normal_map(SkBitmap* bm, const SkIRect& dst);
 
     void make_big_path(SkPath& path);
+
+    // Return a blurred version of 'src'. This doesn't use a separable filter
+    // so it is slow!
+    SkBitmap slow_blur(const SkBitmap& src, float sigma);
+
 }  // namespace sk_tool_utils
 
 #endif  // sk_tool_utils_DEFINED