Allow calling defineCustomElement multiple times with the same element

In case we try to register the element multiple times under the same name
just do nothing. This allows us to not register things by default and
register under the same name in multiple places where needed without
coordination.

packages/common/test/unit.js

@@ -27,6 +27,15 @@ suite('utils', () => {
         expect(node.foo).to.equal(42);
     });
 
+    test('defineCustomElement multiple times', () => {
+        class SomeElement2 extends HTMLElement {
+        }
+        let res = utils.defineCustomElement("test-some-element-2", SomeElement2);
+        assert.isTrue(res);
+        res = utils.defineCustomElement("test-some-element-2", SomeElement2);
+        assert.isTrue(res);
+    });
+
     test('getAPiUrl', () => {
         assert(utils.getAPiUrl().startsWith("http"));
     });

packages/common/utils.js

@@ -103,6 +103,10 @@ export const base64EncodeUnicode = (str) => {
  * @param {object} options 
  */
 export const defineCustomElement = (name, constructor, options) => {
+    // In case the constructor is already defined just do nothing
+    if (customElements.get(name) === constructor) {
+        return true;
+    }
     // Checks taken from https://github.com/webcomponents/webcomponentsjs/blob/master/webcomponents-loader.js
     if (!('attachShadow' in Element.prototype && 'getRootNode' in Element.prototype && window.customElements)) {
         var elements = document.getElementsByTagName(name);