Add new ToolDescriptor constructor to allow subclasses to be in a separate...

Add new ToolDescriptor constructor to allow subclasses to be in a separate file from their describable

core/src/main/java/hudson/tools/ToolDescriptor.java

@@ -54,6 +54,14 @@ public abstract class ToolDescriptor<T extends ToolInstallation> extends Descrip
 
     private T[] installations;
 
+    protected ToolDescriptor() {
+        super();
+    }
+
+    protected ToolDescriptor(Class<T> clazz) {
+        super(clazz);
+    }
+
     /**
      * Configured instances of {@link ToolInstallation}s.
      *