blink_gc_plugin: retire overloaded traceImpl detection and handling.

tools/clang/blink_gc_plugin/tests/legacy_naming/traceimpl_omitted_trace.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_OMITTED_TRACE_H_
 #define TRACEIMPL_OMITTED_TRACE_H_
 
 #include "heap/stubs.h"
 
 namespace blink {
 
 class A : public GarbageCollected<A> {
  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) {}
 };
 
 class B : public A {
   // trace() isn't necessary because we've got nothing to trace here.
 };
 
 class C : public B {
  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 {
     // B::trace() is actually A::trace(), and in certain cases we only get
     // limited information like "there is a function call that will be resolved
     // to A::trace()". We still want to mark B as traced.
     B::trace(visitor);
   }
 };
 
 }
 
 #endif  // TRACEIMPL_OMITTED_TRACE_H_