Move image loading out of C++ into Dart

sky/sdk/lib/framework/net/fetch.dart

Index: sky/sdk/lib/framework/net/fetch.dart
diff --git a/sky/sdk/lib/framework/net/fetch.dart b/sky/sdk/lib/framework/net/fetch.dart
index 720ac4cbc62f832179fa05b5f88f8a4499705d9f..5872af30db747d28bde0c8764cf8b7e515c4a2ee 100644
--- a/sky/sdk/lib/framework/net/fetch.dart
+++ b/sky/sdk/lib/framework/net/fetch.dart
@@ -9,6 +9,7 @@ import 'package:mojo/core.dart' as core;
 import 'package:mojom/mojo/network_service.mojom.dart';
 import 'package:mojom/mojo/url_loader.mojom.dart';
 import 'package:mojom/mojo/url_request.mojom.dart';
+import 'package:mojom/mojo/url_response.mojom.dart';
 
 class Response {
   ByteData body;
@@ -20,23 +21,30 @@ class Response {
   }
 }
 
-Future<Response> fetch(String relativeUrl) async {
-  String url = Uri.base.resolve(relativeUrl).toString();
-
-  var net = new NetworkServiceProxy.unbound();
+Future<UrlResponse> fetch(UrlRequest request) async {
+  NetworkServiceProxy net = new NetworkServiceProxy.unbound();
   shell.requestService("mojo:authenticated_network_service", net);
 
-  var loader = new UrlLoaderProxy.unbound();
+  UrlLoaderProxy loader = new UrlLoaderProxy.unbound();
   net.ptr.createUrlLoader(loader);
 
-  var request = new UrlRequest()
-    ..url = url
-    ..autoFollowRedirects = true;
-  var response = (await loader.ptr.start(request)).response;
+  UrlResponse response = (await loader.ptr.start(request)).response;
 
   loader.close();
   net.close();
+  return response;
+}
+
+Future<UrlResponse> fetchUrl(String relativeUrl) async {
+  String url = Uri.base.resolve(relativeUrl).toString();
+  UrlRequest request = new UrlRequest()
+    ..url = url
+    ..autoFollowRedirects = true;
+  return fetch(request);
+}
 
+Future<Response> fetchBody(String relativeUrl) async {
+  UrlResponse response = await fetchMojo(relativeUrl);
   if (response.body == null) return new Response(null);
 
   ByteData data = await core.DataPipeDrainer.drainHandle(response.body);