RemoveFromGraph on definitions asserts empty use lists.

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
diff --git a/runtime/vm/intermediate_language.h b/runtime/vm/intermediate_language.h
index ddce406c9ae0e62618dcd8af98e332a9bb93e360..f7ce69634851b9e3f96689550c79b5e397fcef22 100644
--- a/runtime/vm/intermediate_language.h
+++ b/runtime/vm/intermediate_language.h
@@ -2372,6 +2372,8 @@ class Definition : public Instruction {
     return changed;
   }
 
+  virtual Instruction* RemoveFromGraph(bool return_previous = true);
+
   UseVal* use_list() { return use_list_; }
   void set_use_list(UseVal* head) {
     ASSERT(head == NULL || head->previous_use() == NULL);