Add flag to skip pipe on select GMs

Confirmed with scroggo@ that these should not be run
with pipe.
Review URL: https://codereview.appspot.com/6405068

git-svn-id: http://skia.googlecode.com/svn/trunk@4698 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gm/aaclip.cpp b/gm/aaclip.cpp
index ba630ca..2988cf3 100644
--- a/gm/aaclip.cpp
+++ b/gm/aaclip.cpp
@@ -183,6 +183,8 @@
         draw_rect_tests(canvas);
     }
 
+    virtual uint32_t onGetFlags() const { return kSkipPipe_Flag; }
+
 private:
     typedef GM INHERITED;
 };