Fix a bug in delete for lookup slots.

src/ia32/codegen-ia32.cc

Index: src/ia32/codegen-ia32.cc
diff --git a/src/ia32/codegen-ia32.cc b/src/ia32/codegen-ia32.cc
index 29c8c0e406cf927e2071f00071ac7e31403d9a02..28ca5d0dfa5db5d613919ce9befd13c605c62702 100644
--- a/src/ia32/codegen-ia32.cc
+++ b/src/ia32/codegen-ia32.cc
@@ -8230,19 +8230,13 @@ void CodeGenerator::VisitUnaryOperation(UnaryOperation* node) {
         return;
 
       } else if (slot != NULL && slot->type() == Slot::LOOKUP) {
-        // Call the runtime to look up the context holding the named
+        // Call the runtime to delete from the context holding the named
         // variable.  Sync the virtual frame eagerly so we can push the
         // arguments directly into place.
         frame_->SyncRange(0, frame_->element_count() - 1);
         frame_->EmitPush(esi);
         frame_->EmitPush(Immediate(variable->name()));
-        Result context = frame_->CallRuntime(Runtime::kLookupContext, 2);
-        ASSERT(context.is_register());
-        frame_->EmitPush(context.reg());
-        context.Unuse();
-        frame_->EmitPush(Immediate(variable->name()));
-        Result answer = frame_->InvokeBuiltin(Builtins::DELETE,
-                                              CALL_FUNCTION, 2);
+        Result answer = frame_->CallRuntime(Runtime::kDeleteContextSlot, 2);
         frame_->Push(&answer);
         return;
       }