Implement spawnDomUri.

tools/dom/src/native_DOMPublic.dart

Index: tools/dom/src/native_DOMPublic.dart
diff --git a/tools/dom/src/native_DOMPublic.dart b/tools/dom/src/native_DOMPublic.dart
index 5044945387b2bc1a40465d218c35733f44ec656a..4034d9165ebd438dde081c59beb1ab02a7f384de 100644
--- a/tools/dom/src/native_DOMPublic.dart
+++ b/tools/dom/src/native_DOMPublic.dart
@@ -4,8 +4,7 @@
 
 part of html;
 
-// This API is exploratory.
-Future<SendPort> spawnDomFunction(Function topLevelFunction) {
+_makeSendPortFuture(spawnRequest) {
   final completer = new Completer<SendPort>();
   final port = new ReceivePort();
   port.receive((result, _) {
@@ -13,10 +12,17 @@ Future<SendPort> spawnDomFunction(Function topLevelFunction) {
     port.close();
   });
   // TODO: SendPort.hashCode is ugly way to access port id.
-  _Utils.spawnDomFunction(topLevelFunction, port.toSendPort().hashCode);
+  spawnRequest(port.toSendPort().hashCode);
   return completer.future;
 }
 
+// This API is exploratory.
+Future<SendPort> spawnDomFunction(Function f) =>
+    _makeSendPortFuture((portId) { _Utils.spawnDomFunction(f, portId); });
+
+Future<SendPort> spawnDomUri(String uri) =>
+    _makeSendPortFuture((portId) { _Utils.spawnDomUri(uri, portId); });
+
 // testRunner implementation.
 // FIXME: provide a separate lib for testRunner.