Detect conflicting variable bindings in harmony mode.

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index 67902cdc32d0f7fa4de0a71c0a69ec878129cd93..e36eb9b32182e481fa8f91e749758e61e228c733 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -408,10 +408,14 @@ class Block: public BreakableStatement {
 
 class Declaration: public AstNode {
  public:
-  Declaration(VariableProxy* proxy, Variable::Mode mode, FunctionLiteral* fun)
+  Declaration(VariableProxy* proxy,
+              Variable::Mode mode,
+              FunctionLiteral* fun,
+              Scope* scope)
       : proxy_(proxy),
         mode_(mode),
-        fun_(fun) {
+        fun_(fun),
+        scope_(scope) {
     ASSERT(mode == Variable::VAR ||
            mode == Variable::CONST ||
            mode == Variable::LET);
@@ -425,11 +429,15 @@ class Declaration: public AstNode {
   Variable::Mode mode() const { return mode_; }
   FunctionLiteral* fun() const { return fun_; }  // may be NULL
   virtual bool IsInlineable() const;
+  Scope* scope() const { return scope_; }
 
  private:
   VariableProxy* proxy_;
   Variable::Mode mode_;
   FunctionLiteral* fun_;
+
+  // Nested scope from which the declaration originated.
+  Scope* scope_;
 };