Make closures optimizable by Crankshaft compiler.

src/variables.h

Index: src/variables.h
diff --git a/src/variables.h b/src/variables.h
index 9e460f7619409ffd8c463fcbcc2a1d3792086e18..e050ed630ad6f4206774ae05b4c40d35a99f2ac0 100644
--- a/src/variables.h
+++ b/src/variables.h
@@ -138,6 +138,9 @@ class Variable: public ZoneObject {
   bool is_accessed_from_inner_scope() const {
     return is_accessed_from_inner_scope_;
   }
+  void MarkAsAccessedFromInnerScope() {
+    is_accessed_from_inner_scope_ = true;
+  }
   bool is_used() { return is_used_; }
   void set_is_used(bool flag) { is_used_ = flag; }
 
@@ -175,6 +178,7 @@ class Variable: public ZoneObject {
   }
 
   Expression* rewrite() const { return rewrite_; }
+  void set_rewrite(Expression* expr) { rewrite_ = expr; }
 
   StaticType* type() { return &type_; }
 
@@ -197,8 +201,6 @@ class Variable: public ZoneObject {
   // Code generation.
   // rewrite_ is usually a Slot or a Property, but may be any expression.
   Expression* rewrite_;
-
-  friend class Scope;  // Has explicit access to rewrite_.
 };