Validate the C++ and managed fields are ordered consistently.

Change-Id: If0d0fcc2ffcc0172bd86fd1714111857af572d6a
diff --git a/src/object.h b/src/object.h
index 0abf444..05071cc 100644
--- a/src/object.h
+++ b/src/object.h
@@ -1043,6 +1043,7 @@
   }
 
  public: // TODO: private
+  // Field order required by test "ValidateFieldOrderOfJavaLangString".
   CharArray* array_;
 
   uint32_t hash_code_;