Represent implicit 'this' binding by 'super' in AST.

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index b1a634edb4c7f02f4dc96658e3e9dba6c5cb9908..1cb9cedfdff4d1d2f23ea81a167aff557924b301 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -362,6 +362,9 @@ class Expression : public AstNode {
   // True if we can prove that the expression is the undefined literal.
   bool IsUndefinedLiteral(Isolate* isolate) const;
 
+  // True iff the expression represents a variable or a property.
+  bool IsVariableProxyOrProperty() const;
+
   // Expression type bounds
   Bounds bounds() const { return bounds_; }
   void set_bounds(Bounds bounds) { bounds_ = bounds; }