Add proper API for creating private symbols wrt a library.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 2c18c69863f752bb40f7a4c3ab289fcf8f1b7067..525dcbeb79e0ddb9ea4fc78b37fb838ad08a1d26 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -4775,6 +4775,10 @@ class String : public Instance {
   static RawString* ToLowerCase(const String& str,
                                 Heap::Space space = Heap::kNew);
 
+  static RawString* StripAccessorPrefix(const String& name);
+  static RawString* StripPrivateMangling(const String& name);
+  static RawString* IdentifierPrettyName(const String& name);
+
   static bool EqualsIgnoringPrivateKey(const String& str1,
                                        const String& str2);