Add Object::IsNullOrUndefined(Isolate*) helper method

src/full-codegen/mips/full-codegen-mips.cc

Index: src/full-codegen/mips/full-codegen-mips.cc
diff --git a/src/full-codegen/mips/full-codegen-mips.cc b/src/full-codegen/mips/full-codegen-mips.cc
index 303932b71e1d04fbbece5ccdbc20a2958a213536..37282824fe620387ca69b5e9a411d79d0b54e244 100644
--- a/src/full-codegen/mips/full-codegen-mips.cc
+++ b/src/full-codegen/mips/full-codegen-mips.cc
@@ -522,10 +522,8 @@ void FullCodeGenerator::TestContext::Plug(Handle<Object> lit) const {
                                           true,
                                           true_label_,
                                           false_label_);
-  DCHECK(lit->IsNull(isolate()) || lit->IsUndefined(isolate()) ||
-         !lit->IsUndetectable());
-  if (lit->IsUndefined(isolate()) || lit->IsNull(isolate()) ||
-      lit->IsFalse(isolate())) {
+  DCHECK(lit->IsNullOrUndefined(isolate()) || !lit->IsUndetectable());
+  if (lit->IsNullOrUndefined(isolate()) || lit->IsFalse(isolate())) {
     if (false_label_ != fall_through_) __ Branch(false_label_);
   } else if (lit->IsTrue(isolate()) || lit->IsJSObject()) {
     if (true_label_ != fall_through_) __ Branch(true_label_);