refactor(dart/transform): Use render Compiler concepts

Update `TemplateCompiler` transform step to use abstractions used by the
render `Compiler`. For example, template code is now loaded via an
instance of `TemplateLoader` and external resources are fetched via an
instance of `XHR`.

modules/angular2/src/dom/browser_adapter.dart

@@ -296,7 +296,9 @@ class BrowserDomAdapter extends GenericBrowserDomAdapter {
   }
   String getEventKey(KeyboardEvent event) {
     int keyCode = event.keyCode;
-    return _keyCodeToKeyMap.containsKey(keyCode) ? _keyCodeToKeyMap[keyCode] : 'Unidentified';
+    return _keyCodeToKeyMap.containsKey(keyCode)
+        ? _keyCodeToKeyMap[keyCode]
+        : 'Unidentified';
   }
   getGlobalEventTarget(String target) {
     if (target == "window") {

modules/angular2/src/dom/html_adapter.dart

@@ -168,9 +168,8 @@ class Html5LibDomAdapter implements DomAdapter {
   getHost(el) {
     throw 'not implemented';
   }
-  clone(node) {
-    throw 'not implemented';
-  }
+  clone(node) => node.clone(true);
+
   hasProperty(element, String name) {
     throw 'not implemented';
   }