Add new GMs to stress rendering of many circles and rrects

Change-Id: I060419bc39484b379329a1691e199d9d3db9c808
Reviewed-on: https://skia-review.googlesource.com/8807
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
diff --git a/gn/gm.gni b/gn/gm.gni
index d9c2565..32c22d7 100644
--- a/gn/gm.gni
+++ b/gn/gm.gni
@@ -188,6 +188,7 @@
   "$_gm/linepaths.cpp",
   "$_gm/localmatriximagefilter.cpp",
   "$_gm/lumafilter.cpp",
+  "$_gm/manypaths.cpp",
   "$_gm/matrixconvolution.cpp",
   "$_gm/matriximagefilter.cpp",
   "$_gm/megalooper.cpp",