fixup field descriptor

core/src/main/java/hudson/node_monitors/ClockMonitor.java

@@ -28,6 +28,8 @@ import hudson.model.Node;
 import hudson.remoting.Callable;
 import hudson.util.ClockDifference;
 import hudson.Extension;
+import org.kohsuke.accmod.Restricted;
+import org.kohsuke.accmod.restrictions.NoExternalUse;
 import org.kohsuke.stapler.StaplerRequest;
 
 import java.io.IOException;
@@ -46,8 +48,19 @@ public class ClockMonitor extends NodeMonitor {
         return DESCRIPTOR.get(c);
     }
 
+    /**
+     * @deprecated as of 2.0
+     *      Don't use this field, use injection.
+     */
+    @Restricted(NoExternalUse.class)
+    public static /*almost final*/ AbstractNodeMonitorDescriptor<ClockDifference> DESCRIPTOR;
+
     @Extension
-    public static final AbstractNodeMonitorDescriptor<ClockDifference> DESCRIPTOR = new AbstractAsyncNodeMonitorDescriptor<ClockDifference>() {
+    public static class DescriptorImpl extends AbstractAsyncNodeMonitorDescriptor<ClockDifference> {
+        public DescriptorImpl() {
+            DESCRIPTOR = this;
+        }
+
         @Override
         protected Callable<ClockDifference,IOException> createCallable(Computer c) {
             Node n = c.getNode();