Don't assume at least one closure function is encountered before tree-shaking. Allow…

runtime/vm/flow_graph_builder.cc

Index: runtime/vm/flow_graph_builder.cc
diff --git a/runtime/vm/flow_graph_builder.cc b/runtime/vm/flow_graph_builder.cc
index da2caaadb36901bf66eba322f7d04cc64e55e28e..e514c2e6d08618d1d32039179cfd6e49ffa810bf 100644
--- a/runtime/vm/flow_graph_builder.cc
+++ b/runtime/vm/flow_graph_builder.cc
@@ -2531,13 +2531,11 @@ static void CollectClosureFunction(const Function& function) {
   if (function.HasCode()) return;
 
   Isolate* isolate = Isolate::Current();
-  if (isolate->collected_closures() == GrowableObjectArray::null()) {
-    isolate->set_collected_closures(
-        GrowableObjectArray::Handle(GrowableObjectArray::New()));
+  if (isolate->collected_closures() != GrowableObjectArray::null()) {

[srdjan, 2015/10/13 21:30:12]

Please add a comment why the check is necessary, even though it is invoked only
when precompiling.

[rmacnak, 2015/10/13 21:55:01]

Done.

+    const GrowableObjectArray& functions =
+        GrowableObjectArray::Handle(isolate, isolate->collected_closures());
+    functions.Add(function);
   }
-  const GrowableObjectArray& functions =
-      GrowableObjectArray::Handle(isolate, isolate->collected_closures());
-  functions.Add(function);
 }