GrpclbLoadBalancer should have full control over the lifecycle of StopWatch

[dapengzhang0]

Would be good to add another GrpclbLoadBalancer constructor without the StopWatch argument. The old constructor is just @VisibleForTesting, and GrpclbLoadBalancerProvider will call the new constructor. In this way, GrpclbLoadBalancer can have full control over the lifecycle of the StopWatch.

[waveywaves]

I would like to start working on this. Anything I need to keep in mind before I start ?

[dapengzhang0]

Thank you for working on this. Nothing special to keep in mind. If you are first-time contributing grpc-java, just not to break the guideline

[waveywaves]

@dapengzhang0 Yes I am a first time contributer to this repo. Thank you for that. Can you assign this to me ?

[dapengzhang0]

I can not assign this to you. Seems you are not in certain user group that is assignable for grpc-java issues.