Expose an lazierRegister flag to defer additional work until first …

…create time. This change requires that a behavior not implement a custom constructor or set the element's `is` property.

src/lib/base.html

@@ -30,9 +30,10 @@
 
     // `this` context is a prototype, not an instance
     registerCallback: function() {
-      // TODO(sjmiles): perhaps this method should be called from polymer-bootstrap?
-      this._desugarBehaviors(); // abstract
-      this._doBehavior('beforeRegister'); // abstract
+      if (!settings.lazierRegister) {
+        this._desugarBehaviors(); // abstract
+        this._doBehavior('beforeRegister'); // abstract
+      }
       this._registerFeatures();  // abstract
       if (!settings.lazyRegister) {
         this.ensureRegisterFinished();
@@ -62,6 +63,13 @@
 
     _ensureRegisterFinished: function(proto) {
       if (proto.__hasRegisterFinished !== proto.is) {
+        // TODO(sorvell): moving all behavior work here means that
+        // custom constructor and is cannot be done in a behavior.
+        // This probably means we need another flag for this
+        if (settings.lazierRegister) {
+          proto._desugarBehaviors(); // abstract
+          proto._doBehavior('beforeRegister'); // abstract
+        }
         proto.__hasRegisterFinished = proto.is;
         if (proto._finishRegisterFeatures) {
           proto._finishRegisterFeatures();