Blink GC plugin: require a trace method if a class derives multiple bases that need tracing.

tools/clang/blink_gc_plugin/tests/class_multiple_trace_bases.cpp

Index: tools/clang/blink_gc_plugin/tests/class_multiple_trace_bases.cpp
diff --git a/tools/clang/blink_gc_plugin/tests/non_virtual_trace.cpp b/tools/clang/blink_gc_plugin/tests/class_multiple_trace_bases.cpp
similarity index 55%
copy from tools/clang/blink_gc_plugin/tests/non_virtual_trace.cpp
copy to tools/clang/blink_gc_plugin/tests/class_multiple_trace_bases.cpp
index b490fc5e403f0e4cccb76b62c2f640047eb30716..73792bfab163db6c0cdada682c61773a8cc7d601 100644
--- a/tools/clang/blink_gc_plugin/tests/non_virtual_trace.cpp
+++ b/tools/clang/blink_gc_plugin/tests/class_multiple_trace_bases.cpp
@@ -2,17 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "non_virtual_trace.h"
+#include "class_multiple_trace_bases.h"
 
 namespace WebCore {
 
-void A::trace(Visitor* visitor)
-{
-}
+void Base::trace(Visitor* visitor) { }
 
-void C::trace(Visitor* visitor)
-{
-    B::trace(visitor);
-}
+void Mixin::trace(Visitor* visitor) { }
+
+// Missing: Derived::trace(visitor)
 
 }