Blink GC plugin: disallow GC derived types as part-object fields.

tools/clang/blink_gc_plugin/tests/part_object_to_gc_derived_class.cpp

Index: tools/clang/blink_gc_plugin/tests/part_object_to_gc_derived_class.cpp
diff --git a/tools/clang/blink_gc_plugin/tests/stack_allocated.cpp b/tools/clang/blink_gc_plugin/tests/part_object_to_gc_derived_class.cpp
similarity index 65%
copy from tools/clang/blink_gc_plugin/tests/stack_allocated.cpp
copy to tools/clang/blink_gc_plugin/tests/part_object_to_gc_derived_class.cpp
index e8a513435f7fdb5194dbaba7438288da6f0fbb0a..6b16e41089baf2aceab15833edd91b1eeaa26dfd 100644
--- a/tools/clang/blink_gc_plugin/tests/stack_allocated.cpp
+++ b/tools/clang/blink_gc_plugin/tests/part_object_to_gc_derived_class.cpp
@@ -2,12 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "stack_allocated.h"
+#include "part_object_to_gc_derived_class.h"
 
 namespace WebCore {
 
-void HeapObject::trace(Visitor* visitor)
+void B::trace(Visitor* visitor)
 {
+    visitor->trace(m_a);
 }
 
 }