Fix memory leak on grpclb shutdown.

src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc

@@ -1036,6 +1036,7 @@ static void glb_shutdown_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
     GRPC_CLOSURE_SCHED(
         exec_ctx, &pp->wrapped_on_complete_arg.wrapper_closure,
         GRPC_ERROR_CREATE_FROM_STATIC_STRING("Channel Shutdown"));
+    gpr_free(pp);
     pp = next;
   }
 
@@ -1044,6 +1045,7 @@ static void glb_shutdown_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
     GRPC_CLOSURE_SCHED(
         exec_ctx, &pping->wrapped_notify_arg.wrapper_closure,
         GRPC_ERROR_CREATE_FROM_STATIC_STRING("Channel Shutdown"));
+    gpr_free(pping);
     pping = next;
   }
 }