In file included from virtual_and_trace_after_dispatch.cpp:5:
./virtual_and_trace_after_dispatch.h:12:1: warning: [blink-gc] Left-most base class 'A' of derived class 'B' must be polymorphic.
class A : public GarbageCollected<A> {
^
./virtual_and_trace_after_dispatch.h:23:1: warning: [blink-gc] Class 'B' contains or inherits virtual methods but implements manual dispatching.
class B : public A {
^
./virtual_and_trace_after_dispatch.h:14:5: note: [blink-gc] Manual dispatch 'Trace' declared here:
    void Trace(Visitor*);
    ^
2 warnings generated.