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

sdk/lib/_internal/pub_generated/test/dart2js/omits_source_map_in_release_test.dart

+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+main() {
+  initConfig();
+  integration("omits source maps from a release build", () {
+    d.dir(
+        appPath,
+        [
+            d.appPubspec(),
+            d.dir(
+                "web",
+                [d.file("main.dart", "void main() => print('hello');")])]).create();
+    schedulePub(
+        args: ["build"],
+        output: new RegExp(r'Built 2 files to "build".'),
+        exitCode: 0);
+    d.dir(
+        appPath,
+        [d.dir('build', [d.dir('web', [d.nothing('main.dart.js.map')])])]).validate();
+  });
+}