BlinkGCPlugin: Fix base class trace call detection in traceImpl().

tools/clang/blink_gc_plugin/tests/traceimpl_error.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_ERROR_H_
 #define TRACEIMPL_ERROR_H_
 
 #include "heap/stubs.h"
 
 namespace blink {
@@ skipping 10 matching lines @@
 
   template <typename VisitorDispatcher>
   void traceImpl(VisitorDispatcher visitor) {
     // Empty; should get complaints from the plugin for untraced x_.
   }
 
  private:
   Member<X> x_;
 };
 
-
 class TraceImplExternWithUntracedMember
     : public GarbageCollected<TraceImplExternWithUntracedMember> {
  public:
   void trace(Visitor* visitor);
 
   template <typename VisitorDispatcher>
   inline void traceImpl(VisitorDispatcher);
 
  private:
   Member<X> x_;
 };
 
+class Base : public GarbageCollected<Base> {
+ public:
+  virtual void trace(Visitor*) {}
+};
+
+class TraceImplInlineWithUntracedBase : public Base {
+ public:
+  void trace(Visitor* visitor) override { traceImpl(visitor); }
+
+  template <typename VisitorDispatcher>
+  void traceImpl(VisitorDispatcher visitor) {
+    // Empty; should get complaints from the plugin for untraced Base.
+  }
+};
+
+class TraceImplExternWithUntracedBase : public Base {
+ public:
+  void trace(Visitor*) override;
+
+  template <typename VisitorDispatcher>
+  void traceImpl(VisitorDispatcher visitor);
+};
+
 }
 
 #endif  // TRACEIMPL_ERROR_H_