Revert "Make window.{undefined,NaN,Infinity} read-only"

src/runtime.cc

 // Copyright 2011 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 1154 matching lines @@
           }
           // Fall-through and introduce the absent property by using
           // SetProperty.
         } else {
           // For const properties, we treat a callback with this name
           // even in the prototype as a conflicting declaration.
           if (is_const_property && (lookup.type() == CALLBACKS)) {
             return ThrowRedeclarationError(isolate, "const", name);
           }
           // Otherwise, we check for locally conflicting declarations.
-          if (is_local && is_const_property) {
+          if (is_local && (is_read_only || is_const_property)) {
             const char* type = (is_read_only) ? "const" : "var";
             return ThrowRedeclarationError(isolate, type, name);
           }
           // The property already exists without conflicting: Go to
           // the next declaration.
           continue;
         }
       }
     } else {
       // Copy the function and update its context. Use it as value.
@@ skipping 213 matching lines @@
       if (type == INTERCEPTOR) {
         HandleScope handle_scope(isolate);
         Handle<JSObject> holder(real_holder);
         PropertyAttributes intercepted = holder->GetPropertyAttribute(*name);
         real_holder = *holder;
         if (intercepted == ABSENT) {
           // The interceptor claims the property isn't there. We need to
           // make sure to introduce it.
           found = false;
         } else if ((intercepted & READ_ONLY) != 0) {
-          // The property is present, but read-only, so we ignore the
-          // redeclaration. However if we found readonly property
+          // The property is present, but read-only. Since we're trying to
+          // overwrite it with a variable declaration we must throw a
+          // re-declaration error.  However if we found readonly property
           // on one of hidden prototypes, just shadow it.
           if (real_holder != isolate->context()->global()) break;
-          return isolate->heap()->undefined_value();
+          return ThrowRedeclarationError(isolate, "const", name);
         }
       }
 
       if (found && !assign) {
         // The global property is there and we're not assigning any value
         // to it. Just return.
         return isolate->heap()->undefined_value();
       }
 
       // Assign the value (or undefined) to the property.
@@ skipping 11342 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(false);
   }
 }
 
 
 } }  // namespace v8::internal