Non-tree-shaking --precompile.

runtime/vm/flow_graph_compiler.cc

Index: runtime/vm/flow_graph_compiler.cc
diff --git a/runtime/vm/flow_graph_compiler.cc b/runtime/vm/flow_graph_compiler.cc
index 4e19dc3d9a9e39b6d3632c4e2dda88a255c66e8e..7eec00cb79685f5ab16698139777b7013fd95de9 100644
--- a/runtime/vm/flow_graph_compiler.cc
+++ b/runtime/vm/flow_graph_compiler.cc
@@ -66,6 +66,7 @@ DECLARE_FLAG(bool, use_field_guards);
 DECLARE_FLAG(bool, use_cha_deopt);
 DECLARE_FLAG(bool, use_osr);
 DECLARE_FLAG(bool, warn_on_javascript_compatibility);
+DECLARE_FLAG(bool, precompile_collect_closures);
 
 
 static void NooptModeHandler(bool value) {
@@ -114,6 +115,7 @@ static void PrecompileModeHandler(bool value) {
     FLAG_lazy_dispatchers = false;
     FLAG_interpret_irregexp = true;
     FLAG_enable_mirrors = false;
+    FLAG_precompile_collect_closures = true;
   }
 }