Add Object::IsNullOrUndefined(Isolate*) helper method

src/inspector/string-util.cc

Index: src/inspector/string-util.cc
diff --git a/src/inspector/string-util.cc b/src/inspector/string-util.cc
index 850aedae51de9a9fff32b08de99797d668dd5d14..31b2db572ddc59694bfcf28d373bb096a9e5eb7a 100644
--- a/src/inspector/string-util.cc
+++ b/src/inspector/string-util.cc
@@ -50,8 +50,7 @@ v8::Local<v8::String> toV8String(v8::Isolate* isolate,
 }
 
 String16 toProtocolString(v8::Local<v8::String> value) {
-  if (value.IsEmpty() || value->IsNull() || value->IsUndefined())
-    return String16();
+  if (value.IsEmpty() || value->IsNullOrUndefined()) return String16();
   std::unique_ptr<UChar[]> buffer(new UChar[value->Length()]);
   value->Write(reinterpret_cast<uint16_t*>(buffer.get()), 0, value->Length());
   return String16(buffer.get(), value->Length());