Heap::AllocateStringFromOneByte() and major part of its callers handlified.

src/string-stream.cc

Index: src/string-stream.cc
diff --git a/src/string-stream.cc b/src/string-stream.cc
index 93eb2229e58db1b817ab187537fe3608c979d86d..e9795adde3653dacd29aad04ea115c4f91293418 100644
--- a/src/string-stream.cc
+++ b/src/string-stream.cc
@@ -265,8 +265,14 @@ void StringStream::OutputToFile(FILE* out) {
 
 
 Handle<String> StringStream::ToString(Isolate* isolate) {
-  return isolate->factory()->NewStringFromUtf8(
+  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;
 }