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

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index 11b07d770a213d570114c54021ef9b5d8e135b53..8711f42384558595a5b487651be8267bedb5fc85 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -3075,8 +3075,8 @@ void FullCodeGenerator::VisitUnaryOperation(UnaryOperation* expr) {
         }
       } 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());