blink_gc_plugin: retire overloaded traceImpl detection and handling.

tools/clang/blink_gc_plugin/tests/traceimpl_overloaded.h

 // Copyright 2015 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 TRACEIMPL_OVERLOADED_H_
 #define TRACEIMPL_OVERLOADED_H_
 
 #include "heap/stubs.h"
 
 namespace blink {
 
 class X : public GarbageCollected<X> {
  public:
   void Trace(Visitor*) {}
-  void Trace(InlinedGlobalMarkingVisitor) {}
 };
 
 class InlinedBase : public GarbageCollected<InlinedBase> {
  public:
-  virtual void Trace(Visitor* visitor) { TraceImpl(visitor); }
-  virtual void Trace(InlinedGlobalMarkingVisitor visitor) {
-    TraceImpl(visitor);
-  }
+  virtual void Trace(Visitor* visitor) { visitor->Trace(x_base_); }
 
  private:
-  template <typename VisitorDispatcher>
-  void TraceImpl(VisitorDispatcher visitor) { visitor->Trace(x_base_); }
-
   Member<X> x_base_;
 };
 
 class InlinedDerived : public InlinedBase {
  public:
-  void Trace(Visitor* visitor) override { TraceImpl(visitor); }
-  void Trace(InlinedGlobalMarkingVisitor visitor) override {
-    TraceImpl(visitor);
-  }
-
- private:
-  template <typename VisitorDispatcher>
-  void TraceImpl(VisitorDispatcher visitor) {
+  void Trace(Visitor* visitor) override {
     visitor->Trace(x_derived_);
     InlinedBase::Trace(visitor);
   }
 
   Member<X> x_derived_;
 };
 
 class ExternBase : public GarbageCollected<ExternBase> {
  public:
   virtual void Trace(Visitor*);
-  virtual void Trace(InlinedGlobalMarkingVisitor);
 
  private:
-  template <typename VisitorDispatcher>
-  void TraceImpl(VisitorDispatcher);
-
   Member<X> x_base_;
 };
 
 class ExternDerived : public ExternBase {
  public:
   void Trace(Visitor*) override;
-  void Trace(InlinedGlobalMarkingVisitor) override;
 
  private:
-  template <typename VisitorDispatcher>
-  void TraceImpl(VisitorDispatcher);
-
   Member<X> x_derived_;
 };
 
 }
 
 #endif  // TRACEIMPL_OVERLOADED_H_