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

tools/clang/blink_gc_plugin/tests/traceimpl_error.cpp

Index: tools/clang/blink_gc_plugin/tests/traceimpl_error.cpp
diff --git a/tools/clang/blink_gc_plugin/tests/traceimpl_error.cpp b/tools/clang/blink_gc_plugin/tests/traceimpl_error.cpp
index e6ab1b1e673b355d54d468e7428aa14fe220803c..041c565e54d45f6651d4c536d09b88f3cfef50f1 100644
--- a/tools/clang/blink_gc_plugin/tests/traceimpl_error.cpp
+++ b/tools/clang/blink_gc_plugin/tests/traceimpl_error.cpp
@@ -16,4 +16,14 @@ inline void TraceImplExternWithUntracedMember::traceImpl(
   // Should get a warning as well.
 }
 
+void TraceImplExternWithUntracedBase::trace(Visitor* visitor) {
+  traceImpl(visitor);
+}
+
+template <typename VisitorDispatcher>
+inline void TraceImplExternWithUntracedBase::traceImpl(
+    VisitorDispatcher visitor) {
+  // Ditto.
+}
+
 }