Mark the functions of closures generated to speed up getField/setField as invisible, just like othe…

runtime/lib/mirrors.cc

Index: runtime/lib/mirrors.cc
diff --git a/runtime/lib/mirrors.cc b/runtime/lib/mirrors.cc
index 7fb8fd01a7a5afcdf9bf57686e15dd3e3d66185c..c4605cf2e031c2a80bbda8d1c550c8849210cb50 100644
--- a/runtime/lib/mirrors.cc
+++ b/runtime/lib/mirrors.cc
@@ -1238,6 +1238,17 @@ DEFINE_NATIVE_ENTRY(Mirrors_evalInLibraryWithPrivateKey, 2) {
     Exceptions::PropagateError(Error::Cast(result));
     UNREACHABLE();
   }
+
+  // Because we currently only use this native for building field extractors and
+  // setters, assume the result is a closure and mark its function as invisible,
+  // so it will not appear in stack traces. Whenever we support
+  // ObjectMirror.evaluate this will need to be separated.
+  ASSERT(Instance::Cast(result).IsClosure());
+  const Function& func =
+      Function::Handle(Closure::function(Instance::Cast(result)));
+  func.set_is_visible(false);
+  func.set_is_debuggable(false);
+
   return result.raw();
 }