Store the async-await compiled pub code directly in the repo.

sdk/lib/_internal/pub_generated/test/serve/does_not_watch_compiled_js_files_test.dart

+library pub_tests;
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import 'utils.dart';
+main() {
+  initConfig();
+  integration("does not watch changes to compiled JS files in the package", () {
+    d.dir(
+        appPath,
+        [d.appPubspec(), d.dir("web", [d.file("index.html", "body")])]).create();
+    pubServe();
+    waitForBuildSuccess();
+    requestShouldSucceed("index.html", "body");
+    d.dir(
+        appPath,
+        [
+            d.dir(
+                "web",
+                [
+                    d.file('file.dart', 'void main() => print("hello");'),
+                    d.file("other.dart.js", "should be ignored"),
+                    d.file("other.dart.js.map", "should be ignored"),
+                    d.file("other.dart.precompiled.js", "should be ignored")])]).create();
+    waitForBuildSuccess();
+    requestShouldSucceed("file.dart", 'void main() => print("hello");');
+    requestShould404("other.dart.js");
+    requestShould404("other.dart.js.map");
+    requestShould404("other.dart.precompiled.js");
+    endPubServe();
+  });
+}