take advantage of the new Descriptor constructor to simplify.

core/src/main/java/hudson/model/DownloadService.java

@@ -53,10 +53,6 @@ import org.kohsuke.stapler.StaplerResponse;
  */
 @Extension
 public class DownloadService extends PageDecorator {
-    public DownloadService() {
-        super(DownloadService.class);
-    }
-
     /**
      * Builds up an HTML fragment that starts all the download jobs.
      */

core/src/main/java/hudson/model/PageDecorator.java

@@ -76,12 +76,18 @@ public abstract class PageDecorator extends Descriptor<PageDecorator> implements
      * @param yourClass
      *      pass-in "this.getClass()" (except that the constructor parameters cannot use 'this',
      *      so you'd have to hard-code the class name.
+     * @deprecated as of 1.425
+     *      Use the default constructor that's less error prone
      */
     protected PageDecorator(Class<? extends PageDecorator> yourClass) {
         super(yourClass);
     }
 
-// this will never work because Descriptor and Describable are the same thing.
+    protected PageDecorator() {
+        super(self());
+    }
+
+    // this will never work because Descriptor and Describable are the same thing.
 //    protected PageDecorator() {
 //    }
 

core/src/main/java/hudson/model/UpdateCenter.java

@@ -1240,9 +1240,6 @@ public class UpdateCenter extends AbstractModelObject implements Saveable {
      */
     @Extension
     public static class PageDecoratorImpl extends PageDecorator {
-        public PageDecoratorImpl() {
-            super(PageDecoratorImpl.class);
-        }
     }
 
     /**

core/src/main/java/hudson/model/UsageStatistics.java

@@ -85,7 +85,6 @@ public class UsageStatistics extends PageDecorator {
      * Creates an instance with a specific public key image.
      */
     public UsageStatistics(String keyImage) {
-        super(UsageStatistics.class);
         this.keyImage = keyImage;
         load();
     }

test/src/test/java/hudson/pages/SystemConfigurationTestCase.java

@@ -65,10 +65,6 @@ public class SystemConfigurationTestCase extends HudsonTestCase {
     private static class PageDecoratorImpl extends PageDecorator {
         private String decoratorId;
 
-        protected PageDecoratorImpl() {
-            super(PageDecoratorImpl.class);
-        }
-
         @Override
         public boolean configure(StaplerRequest req, JSONObject json) throws FormException {
             decoratorId = json.getString("decoratorId");