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

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

Index: sdk/lib/_internal/pub_generated/test/dart2js/source_maps_include_core_libs_test.dart
diff --git a/sdk/lib/_internal/pub_generated/test/dart2js/source_maps_include_core_libs_test.dart b/sdk/lib/_internal/pub_generated/test/dart2js/source_maps_include_core_libs_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..b685b623d59f8187da32f703418e9b7a3b2b867c
--- /dev/null
+++ b/sdk/lib/_internal/pub_generated/test/dart2js/source_maps_include_core_libs_test.dart
@@ -0,0 +1,59 @@
+import 'package:scheduled_test/scheduled_test.dart';
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+main() {
+  initConfig();
+  integration("Dart core libraries are available to source maps", () {
+    d.dir(
+        appPath,
+        [
+            d.appPubspec(),
+            d.dir(
+                "web",
+                [
+                    d.file("main.dart", "main() => new StringBuffer().writeAll(['s']);"),
+                    d.dir(
+                        "sub",
+                        [
+                            d.file(
+                                "main.dart",
+                                "main() => new StringBuffer().writeAll(['s']);")])])]).create();
+    schedulePub(
+        args: ["build", "--mode", "debug"],
+        output: new RegExp(r'Built \d+ files to "build".'),
+        exitCode: 0);
+    d.dir(
+        appPath,
+        [
+            d.dir(
+                "build",
+                [
+                    d.dir(
+                        "web",
+                        [
+                            d.matcherFile(
+                                "main.dart.js.map",
+                                contains(r"packages/$sdk/lib/core/string_buffer.dart")),
+                            d.dir(
+                                "sub",
+                                [
+                                    d.matcherFile(
+                                        "main.dart.js.map",
+                                        contains(r"../packages/$sdk/lib/core/string_buffer.dart"))]),
+                            d.dir(
+                                "packages",
+                                [
+                                    d.dir(
+                                        r"$sdk",
+                                        [
+                                            d.dir(
+                                                "lib",
+                                                [
+                                                    d.dir(
+                                                        r"core",
+                                                        [
+                                                            d.matcherFile(
+                                                                "string_buffer.dart",
+                                                                contains("class StringBuffer"))])])])])])])]).validate();
+  });
+}