Reduce amount of boilerplate associated with bootstrap libraries.

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 343f5979e5eb58182c2db3e23f8a40b3ce59e176..869113f3280f3df8823fc5589b86e4c979b35d39 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -5831,6 +5831,7 @@ DART_EXPORT Dart_Handle Dart_FinalizeLoading(bool complete_futures) {
     I->debugger()->NotifyDoneLoading();
   }
 
+#if !defined(PRODUCT)
   if (FLAG_enable_mirrors) {
     // Notify mirrors that MirrorSystem.libraries needs to be recomputed.
     const Library& libmirrors = Library::Handle(Z, Library::MirrorsLibrary());
@@ -5839,6 +5840,7 @@ DART_EXPORT Dart_Handle Dart_FinalizeLoading(bool complete_futures) {
     ASSERT(!dirty_bit.IsNull() && dirty_bit.is_static());
     dirty_bit.SetStaticValue(Bool::True());
   }
+#endif
 
   if (complete_futures) {
     const Library& corelib = Library::Handle(Z, Library::CoreLibrary());