Handlification TODOs in scanner and string stream resolved.

src/string-stream.cc

Index: src/string-stream.cc
diff --git a/src/string-stream.cc b/src/string-stream.cc
index e9795adde3653dacd29aad04ea115c4f91293418..25e340b4a563323f7a830ee73033161572906bb3 100644
--- a/src/string-stream.cc
+++ b/src/string-stream.cc
@@ -265,14 +265,8 @@ void StringStream::OutputToFile(FILE* out) {
 
 
 Handle<String> StringStream::ToString(Isolate* isolate) {
-  MaybeHandle<String> maybe_result = isolate->factory()->NewStringFromUtf8(
-      Vector<const char>(buffer_, length_));
-
-  // TODO(ishell): Temporarily returning null handle from here. I will proceed
-  // with maybehandlification in next CLs.
-  Handle<String> result;
-  if (!maybe_result.ToHandle(&result)) return Handle<String>();
-  return result;
+  return isolate->factory()->NewStringFromUtf8(
+      Vector<const char>(buffer_, length_)).ToHandleChecked();
 }