Add IsStackAllocated helper for variables.

src/variables.h

Index: src/variables.h
diff --git a/src/variables.h b/src/variables.h
index 1751f1285dd7dbaf1817411c8da3ccb1e182115b..a68aa337f44ba48694d12443a61b23bb8817047f 100644
--- a/src/variables.h
+++ b/src/variables.h
@@ -146,6 +146,8 @@ class Variable: public ZoneObject {
     return !is_this() && name().is_identical_to(n);
   }
 
+  bool IsStackAllocated() const;
+
   bool is_dynamic() const {
     return (mode_ == DYNAMIC ||
             mode_ == DYNAMIC_GLOBAL ||