blink_gc_plugin: retire overloaded traceImpl detection and handling.

tools/clang/blink_gc_plugin/tests/traceimpl_dependent_scope.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_DEPENDENT_SCOPE_H_
 #define TRACEIMPL_DEPENDENT_SCOPE_H_
 
 #include "heap/stubs.h"
 
 namespace blink {
 
 class X : public GarbageCollected<X> {
  public:
   virtual void Trace(Visitor*) {}
 };
 
 template <typename T>
 class Base : public GarbageCollected<Base<T> > {
  public:
-  virtual void Trace(Visitor* visitor) { TraceImpl(visitor); }
-  virtual void Trace(InlinedGlobalMarkingVisitor visitor) {
-    TraceImpl(visitor);
-  }
-
- private:
-  template <typename VisitorDispatcher>
-  void TraceImpl(VisitorDispatcher visitor) {}
+  virtual void Trace(Visitor* visitor) {}
 };
 
 template <typename T>
 class Derived : public Base<T> {
  public:
-  void Trace(Visitor* visitor) override { TraceImpl(visitor); }
-  void Trace(InlinedGlobalMarkingVisitor visitor) override {
-    TraceImpl(visitor);
-  }
-
- private:
-  template <typename VisitorDispatcher>
-  void TraceImpl(VisitorDispatcher visitor) {
-    Base<T>::Trace(visitor);
-  }
+  void Trace(Visitor* visitor) override { Base<T>::Trace(visitor); }
 };
 
 template <typename T>
 class DerivedMissingTrace : public Base<T> {
  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 {
     // Missing Base<T>::Trace(visitor).
   }
 };
 
 }
 
 #endif  // TRACEIMPL_DEPENDENT_SCOPE_H_