core,xds: Fix backend_service plumbing for subchannel metrics#12735

becomeStar wants to merge 1 commit intogrpc:mastergrpc/grpc-java:masterfrom

becomeStar:fix/12432-backend-service-subchannel-metricsbecomeStar/grpc-java:fix/12432-backend-service-subchannel-metricsCopy head branch name to clipboard