Add some support for the code-point code-unit distinction.

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index fb992035d27d509583377477b25f7cb44354c09a..514d5ff43d1f95fb662bf019b2573b363664a024 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -1579,7 +1579,9 @@ DART_EXPORT Dart_Handle Dart_NewStringFromUTF32(const uint32_t* utf32_array,
     RETURN_NULL_ERROR(utf32_array);
   }
   CHECK_LENGTH(length, String::kMaxElements);
-  return Api::NewHandle(isolate, String::New(utf32_array, length));
+  return Api::NewHandle(
+      isolate,
+      String::New(reinterpret_cast<const int32_t*>(utf32_array), length));
 }