[parsing]: eval/arguments parameter names are ok in sloppy mode

src/scopes.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_SCOPES_H_
 #define V8_SCOPES_H_
 
 #include "src/ast.h"
 #include "src/zone.h"
 
@@ skipping 449 matching lines @@
   // Strict mode support.
   bool IsDeclared(const AstRawString* name) {
     // During formal parameter list parsing the scope only contains
     // two variables inserted at initialization: "this" and "arguments".
     // "this" is an invalid parameter name and "arguments" is invalid parameter
     // name in strict mode. Therefore looking up with the map which includes
     // "this" and "arguments" in addition to all formal parameters is safe.
     return variables_.Lookup(name) != NULL;
   }
 
+  bool IsDeclaredParameter(const AstRawString* name) {
+    // If IsSimpleParameterList is false, duplicate parameters are not allowed,
+    // however `arguments` may be allowed if function is not strict code. Thus,
+    // the assumptions explained above do not hold.
+    return params_.Contains(variables_.Lookup(name));
+  }
+
   // ---------------------------------------------------------------------------
   // Debugging.
 
 #ifdef DEBUG
   void Print(int n = 0);  // n = indentation; n < 0 => don't print recursively
 #endif
 
   // ---------------------------------------------------------------------------
   // Implementation.
  protected:
@@ skipping 211 matching lines @@
                    Scope* outer_scope,
                    Handle<ScopeInfo> scope_info);
 
   AstValueFactory* ast_value_factory_;
   Zone* zone_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_SCOPES_H_