feat(view): add support for components that use shadow dom emulation

modules/facade/src/dom.dart

@@ -47,6 +47,9 @@ class DOM {
   static List<Node> childNodes(el) {
     return el.childNodes;
   }
+  static clearNodes(el) {
+    el.nodes = [];
+  }
   static appendChild(el, node) {
     el.append(node);
   }

modules/facade/src/dom.es6

@@ -40,6 +40,9 @@ export class DOM {
   static childNodes(el):NodeList {
     return el.childNodes;
   }
+  static clearNodes(el) {
+    el.innerHTML = "";
+  }
   static appendChild(el, node) {
     el.appendChild(node);
   }