Allow lexically declared "arguments" in function scope in sloppy mode.

src/ast/scopes.h

Index: src/ast/scopes.h
diff --git a/src/ast/scopes.h b/src/ast/scopes.h
index 5f0ebb9ed50dab8a625d9368290a05cf199aca58..c45894c0776cbd086a932bfd7211b0ad6c58177c 100644
--- a/src/ast/scopes.h
+++ b/src/ast/scopes.h
@@ -626,6 +626,7 @@ class DeclarationScope : public Scope {
   void set_asm_function() { asm_module_ = true; }
 
   void DeclareThis(AstValueFactory* ast_value_factory);
+  void DeclareArguments(AstValueFactory* ast_value_factory);
   void DeclareDefaultFunctionVariables(AstValueFactory* ast_value_factory);
 
   // This lookup corresponds to a lookup in the "intermediate" scope sitting