Implement ES5 erratum: global declarations shadow inherited properties.

src/parser.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2236 matching lines @@
     }
 
     // Make sure that 'const x' and 'let x' initialize 'x' to undefined.
     if (value == NULL && needs_init) {
       value = GetLiteralUndefined();
     }
 
     // Global variable declarations must be compiled in a specific
     // way. When the script containing the global variable declaration
     // is entered, the global variable must be declared, so that if it
-    // doesn't exist (not even in a prototype of the global object) it
+    // doesn't exist (on the global object itself, see ES5 errata) it
     // gets created with an initial undefined value. This is handled
     // by the declarations part of the function representing the
     // top-level global code; see Runtime::DeclareGlobalVariable. If
     // it already exists (in the object or in a prototype), it is
     // *not* touched until the variable declaration statement is
     // executed.
     //
     // Executing the variable declaration statement will always
     // guarantee to give the global object a "local" variable; a
     // variable defined in the global object and not in any
@@ skipping 3747 matching lines @@
       ASSERT(info->isolate()->has_pending_exception());
     } else {
       result = parser.ParseProgram(info);
     }
   }
   info->SetFunction(result);
   return (result != NULL);
 }
 
 } }  // namespace v8::internal