Fix telemetry registrations to go eagerly

lib/mixins/element-mixin.html

@@ -303,10 +303,6 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
        */
      static _finalizeClass() {
         super._finalizeClass();
-        if (this.hasOwnProperty(
-          JSCompiler_renameProperty('is', this)) &&  this.is) {
-          Polymer.telemetry.register(this.prototype);
-        }
         const observers = ownObservers(this);
         if (observers) {
           this.createObservers(observers, this._properties);

lib/mixins/properties-mixin.html

@@ -116,6 +116,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
        * @suppress {missingProperties} Interfaces in closure do not inherit statics, but classes do
        */
       static get observedAttributes() {
+        Polymer.telemetry.register(this.prototype);
         const props = this._properties;
         return props ? Object.keys(props).map(p => this.attributeNameForProperty(p)) : [];
       }