Fix for bug http://code.google.com/p/v8/issues/detail?id=1176.

src/x64/full-codegen-x64.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 3057 matching lines @@
           context()->Plug(false);
         } else {
           VisitForStackValue(prop->obj());
           VisitForStackValue(prop->key());
           __ Push(Smi::FromInt(strict_mode_flag()));
           __ InvokeBuiltin(Builtins::DELETE, CALL_FUNCTION);
           context()->Plug(rax);
         }
       } else if (var != NULL) {
         // Delete of an unqualified identifier is disallowed in strict mode
-        // so this code can only be reached in non-strict mode.
-        ASSERT(strict_mode_flag() == kNonStrictMode);
+        // but "delete this" is.
+        ASSERT(strict_mode_flag() == kNonStrictMode || var->is_this());
         if (var->is_global()) {
           __ push(GlobalObjectOperand());
           __ Push(var->name());
           __ Push(Smi::FromInt(kNonStrictMode));
           __ InvokeBuiltin(Builtins::DELETE, CALL_FUNCTION);
           context()->Plug(rax);
         } else if (var->AsSlot() != NULL &&
                    var->AsSlot()->type() != Slot::LOOKUP) {
           // Result of deleting non-global, non-dynamic variables is false.
           // The subexpression does not have side effects.
@@ skipping 678 matching lines @@
   __ ret(0);
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64