Secure Shell can't run an arbitrary ProxyCommand, because that would violate Chrome's sandboxing of Chrome extensions (or of Chrome apps or websites/webapps).
You can connect to jumpserver in one Secure Shell session with a port forward to dbserver:22 (e.g. -L12345:dbserver:22), then use another Secure Shell session to connect via the forwarded port (e.g. connect to localhost:12345).
You could use ssh with ProxyCommand from Crostini, if Crostini is available on your device.
You can connect to jumpserver from Secure Shell and then just run "ssh dbserver" from there. With this option, if you need port forwarding through dbserver you would have to configure each forwarded port at both the jumpserver and dbserver layers though.
If you have administrative control over jumpserver, there more options you could setup.