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

src/x64/codegen-x64.cc

Index: src/x64/codegen-x64.cc
diff --git a/src/x64/codegen-x64.cc b/src/x64/codegen-x64.cc
index 150ed664b0a4b6c300e0551f54c4fa1bdd212d92..3a6491bd64d4f99aa144168ddafb20f6a068ea67 100644
--- a/src/x64/codegen-x64.cc
+++ b/src/x64/codegen-x64.cc
@@ -7239,8 +7239,8 @@ void CodeGenerator::VisitUnaryOperation(UnaryOperation* node) {
     Variable* variable = node->expression()->AsVariableProxy()->AsVariable();
     if (variable != 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 || variable->is_this());
       Slot* slot = variable->AsSlot();
       if (variable->is_global()) {
         LoadGlobal();
@@ -7249,7 +7249,6 @@ void CodeGenerator::VisitUnaryOperation(UnaryOperation* node) {
         Result answer = frame_->InvokeBuiltin(Builtins::DELETE,
                                               CALL_FUNCTION, 3);
         frame_->Push(&answer);
-        return;
 
       } else if (slot != NULL && slot->type() == Slot::LOOKUP) {
         // Call the runtime to delete from the context holding the named
@@ -7260,13 +7259,11 @@ void CodeGenerator::VisitUnaryOperation(UnaryOperation* node) {
         frame_->EmitPush(variable->name());
         Result answer = frame_->CallRuntime(Runtime::kDeleteContextSlot, 2);
         frame_->Push(&answer);
-        return;
+      } else {
+        // Default: Result of deleting non-global, not dynamically
+        // introduced variables is false.
+        frame_->Push(Factory::false_value());
       }
-
-      // Default: Result of deleting non-global, not dynamically
-      // introduced variables is false.
-      frame_->Push(Factory::false_value());
-
     } else {
       // Default: Result of deleting expressions is true.
       Load(node->expression());  // may have side-effects