Revert of GC plugin: improve error reporting when tracing illegal fields.

tools/clang/blink_gc_plugin/tests/fields_illegal_tracing.h

-// 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 FIELDS_ILLEGAL_TRACING_H_
-#define FIELDS_ILLEGAL_TRACING_H_
-
-#include "heap/stubs.h"
-
-namespace blink {
-
-namespace bar {
-
-// check that (only) std::unique_ptr<> is reported
-// as an illegal smart pointer type.
-template<typename T> class unique_ptr {
-public:
-    ~unique_ptr() { }
-    operator T*() const { return 0; }
-    T* operator->() { return 0; }
-
-    void trace(Visitor* visitor)
-    {
-    }
-};
-
-}
-
-class HeapObject;
-class PartObject;
-
-class PartObject {
-    DISALLOW_ALLOCATION();
-public:
-    void trace(Visitor*);
-private:
-    OwnPtr<HeapObject> m_obj1;
-    RefPtr<HeapObject> m_obj2;
-    bar::unique_ptr<HeapObject> m_obj3;
-    std::unique_ptr<HeapObject> m_obj4;
-};
-
-class HeapObject : public GarbageCollectedFinalized<HeapObject> {
-public:
-    void trace(Visitor*);
-private:
-    PartObject m_part;
-    OwnPtr<HeapObject> m_obj1;
-    RefPtr<HeapObject> m_obj2;
-    bar::unique_ptr<HeapObject> m_obj3;
-    std::unique_ptr<HeapObject> m_obj4;
-};
-
-}
-
-#endif