Compile spawnUri entrypoints to JS with pub build/serve.

sdk/lib/_internal/pub/test/transformer/dart2js/converts_isolate_entrypoint_in_web_test.dart

Index: sdk/lib/_internal/pub/test/transformer/dart2js/converts_isolate_entrypoint_in_web_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/dart2js/converts_entrypoint_in_web_test.dart b/sdk/lib/_internal/pub/test/transformer/dart2js/converts_isolate_entrypoint_in_web_test.dart
similarity index 68%
copy from sdk/lib/_internal/pub/test/transformer/dart2js/converts_entrypoint_in_web_test.dart
copy to sdk/lib/_internal/pub/test/transformer/dart2js/converts_isolate_entrypoint_in_web_test.dart
index 90ad051152442fcfc8c1634457b5c1b4e56425f1..24302733548c72eccaac9ec3aa8917fee84c83c1 100644
--- a/sdk/lib/_internal/pub/test/transformer/dart2js/converts_entrypoint_in_web_test.dart
+++ b/sdk/lib/_internal/pub/test/transformer/dart2js/converts_isolate_entrypoint_in_web_test.dart
@@ -12,16 +12,17 @@ import '../../serve/utils.dart';
 
 main() {
   initConfig();
-  integration("converts a Dart entrypoint in web to JS", () {
+  integration("converts a Dart isolate entrypoint in web to JS", () {
     d.dir(appPath, [
       d.appPubspec(),
       d.dir("web", [
-        d.file("main.dart", "void main() => print('hello');")
+        d.file("isolate.dart", "void main(List<String> args, SendPort "
+            "sendPort) => print('hello');")
       ])
     ]).create();
 
     pubServe();
-    requestShouldSucceed("main.dart.js", contains("hello"));
+    requestShouldSucceed("isolate.dart.js", contains("hello"));
     endPubServe();
   });
 }