Do not hide membership of implementation classes in dart:core.

runtime/lib/mirrors.cc

Index: runtime/lib/mirrors.cc
diff --git a/runtime/lib/mirrors.cc b/runtime/lib/mirrors.cc
index 21000a9a7c705c9582ab568441d843694c0a9119..07029a2e6af5d6917e9b8fcb9a374ff571385156 100644
--- a/runtime/lib/mirrors.cc
+++ b/runtime/lib/mirrors.cc
@@ -1117,11 +1117,10 @@ DEFINE_NATIVE_ENTRY(LibraryMirror_members, 2) {
     entry = entries.GetNext();
     if (entry.IsClass()) {
       const Class& klass = Class::Cast(entry);
-      // We filter out implementation classes like Smi, Mint, Bignum,
-      // OneByteString; function signature classes; and dynamic.
+      // We filter out function signature classes and dynamic.
+      // TODO(12478): Should not need to filter out dynamic.
       if (!klass.IsCanonicalSignatureClass() &&
-          !klass.IsDynamicClass() &&
-          !RawObject::IsImplementationClassId(klass.id())) {
+          !klass.IsDynamicClass()) {
         type = klass.RareType();
         member_mirror = CreateClassMirror(klass,
                                           type,