Fixes a couple problems with GC of unoptimized code.

runtime/vm/visitor.h

Index: runtime/vm/visitor.h
===================================================================
--- runtime/vm/visitor.h	(revision 30598)
+++ runtime/vm/visitor.h	(working copy)
@@ -6,6 +6,7 @@
 #define VM_VISITOR_H_
 
 #include "vm/globals.h"
+#include "vm/growable_array.h"
 
 namespace dart {
 
@@ -24,6 +25,11 @@
   // Range of pointers to visit 'first' <= pointer <= 'last'.
   virtual void VisitPointers(RawObject** first, RawObject** last) = 0;
 
+  virtual bool visit_function_code() const { return true; }
+  virtual GrowableArray<RawFunction*>* skipped_code_functions() {
+    return NULL;
+  }
+
   // len argument is the number of pointers to visit starting from 'p'.
   void VisitPointers(RawObject** p, intptr_t len) {
     VisitPointers(p, (p + len - 1));