Address review comments in commited cl (issue 10460002).

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
===================================================================
--- runtime/vm/intermediate_language.h	(revision 8115)
+++ runtime/vm/intermediate_language.h	(working copy)
@@ -1008,13 +1008,14 @@
 
 class CreateClosureComp : public Computation {
  public:
-  // 'type_arguments' is null if function() does not require type arguments.
   CreateClosureComp(ClosureNode* node,
                     intptr_t try_index,
                     Value* type_arguments)
       : ast_node_(*node),
         try_index_(try_index),
-        type_arguments_(type_arguments) {}
+        type_arguments_(type_arguments) {
+    ASSERT(type_arguments != NULL);
+  }
 
   DECLARE_COMPUTATION(CreateClosure)