Fix a bug in delete for lookup slots.

src/arm/codegen-arm.cc

Index: src/arm/codegen-arm.cc
diff --git a/src/arm/codegen-arm.cc b/src/arm/codegen-arm.cc
index 2fa071195953fa7b28aaa86734012455d5d68541..c5a2b2bbaa461262d80bbd433aa3a8098998ae7a 100644
--- a/src/arm/codegen-arm.cc
+++ b/src/arm/codegen-arm.cc
@@ -5849,14 +5849,10 @@ void CodeGenerator::VisitUnaryOperation(UnaryOperation* node) {
         frame_->EmitPush(r0);
 
       } else if (slot != NULL && slot->type() == Slot::LOOKUP) {
-        // lookup the context holding the named variable
+        // Delete from the context holding the named variable.
         frame_->EmitPush(cp);
         frame_->EmitPush(Operand(variable->name()));
-        frame_->CallRuntime(Runtime::kLookupContext, 2);
-        // r0: context
-        frame_->EmitPush(r0);
-        frame_->EmitPush(Operand(variable->name()));
-        frame_->InvokeBuiltin(Builtins::DELETE, CALL_JS, 2);
+        frame_->CallRuntime(Runtime::kDeleteContextSlot, 2);
         frame_->EmitPush(r0);
 
       } else {