Support cross-origin requests to pub serve.

sdk/lib/_internal/pub_generated/lib/src/barback/barback_server.dart

Index: sdk/lib/_internal/pub_generated/lib/src/barback/barback_server.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/barback/barback_server.dart b/sdk/lib/_internal/pub_generated/lib/src/barback/barback_server.dart
index 49bea930fe3c81d6c2816afa7cbbce832be70c24..24658e22592e090fdf4139ee289248bc70c63f1d 100644
--- a/sdk/lib/_internal/pub_generated/lib/src/barback/barback_server.dart
+++ b/sdk/lib/_internal/pub_generated/lib/src/barback/barback_server.dart
@@ -144,6 +144,14 @@ class BarbackServer extends BaseServer<BarbackServerResult> {
 
       addResult(new BarbackServerResult._failure(request.url, id, error));
       return notFound(request, asset: id);
+    }).then((response) {
+      // Allow requests of any origin to access "pub serve". This is useful for
+      // running "pub serve" in parallel with another development server. Since
+      // "pub serve" is only used as a development server and doesn't require
+      // any sort of credentials anyway, this is secure.
+      return response.change(headers: const {
+        "Access-Control-Allow-Origin": "*"
+      });
     });
   }