Fix capturing variables in optimized compilations

runtime/vm/parser.h

Index: runtime/vm/parser.h
diff --git a/runtime/vm/parser.h b/runtime/vm/parser.h
index 84301f258a4ef2d2d42c872e2d6da2c976aefdcc..e9f5bc01ac0d6f3777a31e36fe4c84bf9d768c8a 100644
--- a/runtime/vm/parser.h
+++ b/runtime/vm/parser.h
@@ -338,6 +338,10 @@ class Parser : public ValueObject {
   // current_function(), but is greater than zero while parsing the body of
   // local functions nested in current_function().
 
+  // FunctionLevel is 0 when parsing code of current_function(), and denotes
+  // the relative nesting level when parsing a nested function.
+  int FunctionLevel() const;
+
   // The class being parsed.
   const Class& current_class() const;
   void set_current_class(const Class& value);