In file included from trace_wrapper.cpp:5:
./trace_wrapper.h:18:3: warning: [blink-gc] Class 'A' has untraced fields that require tracing.
  void Trace(Visitor*) const {
  ^
./trace_wrapper.h:23:3: note: [blink-gc] Untraced field 'str_' declared here:
  TraceWrapperV8Reference<v8::String> str_;
  ^
./trace_wrapper.h:37:3: warning: [blink-gc] Base class 'B' of derived class 'C' requires tracing.
  void TraceAfterDispatch(Visitor*) const {
  ^
./trace_wrapper.h:37:3: warning: [blink-gc] Class 'C' has untraced fields that require tracing.
./trace_wrapper.h:42:3: note: [blink-gc] Untraced field 'str_' declared here:
  TraceWrapperV8Reference<v8::String> str_;
  ^
3 warnings generated.