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

runtime/vm/debugger.cc

Index: runtime/vm/debugger.cc
diff --git a/runtime/vm/debugger.cc b/runtime/vm/debugger.cc
index 96019a94589029d32599d07702840a0ca38c974e..04da04fa72d3e3565176b815c1c814f76e92910a 100644
--- a/runtime/vm/debugger.cc
+++ b/runtime/vm/debugger.cc
@@ -1230,7 +1230,7 @@ void Debugger::CollectLibraryFields(const GrowableObjectArray& field_list,
       cls = field.owner();
       ASSERT(field.is_static());
       field_name = field.name();
-      if ((field_name.CharAt(0) == '_') && !include_private_fields) {
+      if ((field_name.CodeUnitAt(0) == '_') && !include_private_fields) {
         // Skip library-private field.
         continue;
       }