Blink GC plugin: disallow pure-virtual trace methods.

tools/clang/blink_gc_plugin/tests/pure_virtual_trace.h

 // Copyright 2014 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 PURE_VIRTUAL_BASE_H_
-#define PURE_VIRTUAL_BASE_H_
+#ifndef PURE_VIRTUAL_TRACE_H_
+#define PURE_VIRTUAL_TRACE_H_
 
 #include "heap/stubs.h"
 
 namespace WebCore {
 
 class A : public GarbageCollected<A> {
 public:
     virtual void trace(Visitor*) = 0;
 };
 
-class B : public A {
-public:
-    // Does not need a trace method.
-};
-
-class C : public B {
-public:
-    void trace(Visitor*);
-private:
-    Member<A> m_a;
-};
-
 }
 
 #endif