Make Client polymorphic by adding a virtual destructor

PiperOrigin-RevId: 675145888
Change-Id: Iad1821642e73db27c522baf4efe64dad78acbf7d

sandboxed_api/sandbox2/client.h

@@ -43,6 +43,7 @@ class Client {
  static constexpr uint32_t kSandbox2ClientUnotify = 0x0A0B0C03;
 
  explicit Client(Comms* comms);
+ virtual ~Client() = default;
 
  Client(const Client&) = delete;
  Client& operator=(const Client&) = delete;