util: MultiChildLB children know if they are active

No need to look up in the map to see if they are still a child.

Author: ejona86

util/src/main/java/io/grpc/util/MultiChildLoadBalancer.java

@@ -414,7 +414,7 @@ protected class ChildLbStateHelper extends ForwardingLoadBalancerHelper {
       @Override
       public void updateBalancingState(final ConnectivityState newState,
           final SubchannelPicker newPicker) {
-        if (!childLbStates.containsKey(key)) {
+        if (currentState == SHUTDOWN) {
           return;
         }
 

xds/src/main/java/io/grpc/xds/ClusterManagerLoadBalancer.java

@@ -260,16 +260,16 @@ private class ClusterManagerChildHelper extends ChildLbStateHelper {
       @Override
       public void updateBalancingState(final ConnectivityState newState,
                                        final SubchannelPicker newPicker) {
-        // If we are already in the process of resolving addresses, the overall balancing state
-        // will be updated at the end of it, and we don't need to trigger that update here.
-        if (getChildLbState(getKey()) == null) {
+        if (getCurrentState() == ConnectivityState.SHUTDOWN) {
           return;
         }
 
         // Subchannel picker and state are saved, but will only be propagated to the channel
         // when the child instance exits deactivated state.
         setCurrentState(newState);
         setCurrentPicker(newPicker);
+        // If we are already in the process of resolving addresses, the overall balancing state
+        // will be updated at the end of it, and we don't need to trigger that update here.
         if (deletionTimer == null && !resolvingAddresses) {
           updateOverallBalancingState();
         }