Update from https://crrev.com/318214

tools/clang/blink_gc_plugin/tests/trace_after_dispatch_impl.cpp

+// 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.
+
+#include "trace_after_dispatch_impl.h"
+
+namespace blink {
+
+void TraceAfterDispatchInlinedBase::trace(Visitor* visitor) {
+  // Implement a simple form of manual dispatching, because BlinkGCPlugin gets
+  // angry if dispatching statements are missing.
+  //
+  // This function has to be implemented out-of-line, since we need to know the
+  // definition of derived classes here.
+  if (tag_ == DERIVED) {
+    static_cast<TraceAfterDispatchInlinedDerived*>(this)->traceAfterDispatch(
+        visitor);
+  } else {
+    traceAfterDispatch(visitor);
+  }
+}
+
+void TraceAfterDispatchExternBase::trace(Visitor* visitor) {
+  if (tag_ == DERIVED) {
+    static_cast<TraceAfterDispatchExternDerived*>(this)->traceAfterDispatch(
+        visitor);
+  } else {
+    traceAfterDispatch(visitor);
+  }
+}
+
+void TraceAfterDispatchExternBase::traceAfterDispatch(Visitor* visitor) {
+  traceAfterDispatchImpl(visitor);
+}
+
+template <typename VisitorDispatcher>
+inline void TraceAfterDispatchExternBase::traceAfterDispatchImpl(
+    VisitorDispatcher visitor) {
+  visitor->trace(x_base_);
+}
+
+void TraceAfterDispatchExternDerived::traceAfterDispatch(Visitor* visitor) {
+  traceAfterDispatchImpl(visitor);
+}
+
+template <typename VisitorDispatcher>
+inline void TraceAfterDispatchExternDerived::traceAfterDispatchImpl(
+    VisitorDispatcher visitor) {
+  visitor->trace(x_derived_);
+  TraceAfterDispatchExternBase::traceAfterDispatch(visitor);
+}
+
+}