GC plugin: improve error reporting when tracing illegal fields.

tools/clang/blink_gc_plugin/tests/persistent_no_trace.h

Index: tools/clang/blink_gc_plugin/tests/persistent_no_trace.h
diff --git a/tools/clang/blink_gc_plugin/tests/destructor_in_nonfinalized_class.h b/tools/clang/blink_gc_plugin/tests/persistent_no_trace.h
similarity index 50%
copy from tools/clang/blink_gc_plugin/tests/destructor_in_nonfinalized_class.h
copy to tools/clang/blink_gc_plugin/tests/persistent_no_trace.h
index f3fa506a4ca05277cdc729c09aca95b03731f0db..c8beb9962c2c9f298429a8dcede29c81bdf4ae10 100644
--- a/tools/clang/blink_gc_plugin/tests/destructor_in_nonfinalized_class.h
+++ b/tools/clang/blink_gc_plugin/tests/persistent_no_trace.h
@@ -1,9 +1,9 @@
-// Copyright 2014 The Chromium Authors. All rights reserved.
+// Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef DESTRUCTOR_IN_NONFINALIZED_CLASS_H_
-#define DESTRUCTOR_IN_NONFINALIZED_CLASS_H_
+#ifndef PERSISTENT_NO_TRACE_H_
+#define PERSISTENT_NO_TRACE_H_
 
 #include "heap/stubs.h"
 
@@ -11,10 +11,10 @@ namespace blink {
 
 class HeapObject : public GarbageCollected<HeapObject> {
 public:
-    ~HeapObject();
     void trace(Visitor*);
 private:
-    Member<HeapObject> m_obj;
+    CrossThreadPersistent<HeapObject> m_crossThreadPersistent;
+    CrossThreadWeakPersistent<HeapObject> m_crossThreadWeakPersistent;
 };
 
 }