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

sdk/lib/_internal/pub_generated/test/snapshot/recompiles_if_the_sdk_is_out_of_date_test.dart

+library pub_tests;
+import 'package:path/path.dart' as p;
+import 'package:scheduled_test/scheduled_test.dart';
+import 'package:scheduled_test/scheduled_stream.dart';
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+main() {
+  initConfig();
+  integration(
+      "creates a snapshot for an immediate dependency's executables",
+      () {
+    servePackages((builder) {
+      builder.serve(
+          "foo",
+          "5.6.7",
+          contents: [
+              d.dir("bin", [d.file("hello.dart", "void main() => print('hello!');")])]);
+    });
+    d.appDir({
+      "foo": "5.6.7"
+    }).create();
+    pubGet(output: contains("Precompiled foo:hello."));
+    d.dir(
+        p.join(appPath, '.pub', 'bin'),
+        [d.dir('foo', [d.outOfDateSnapshot('hello.dart.snapshot')])]).create();
+    var process = pubRun(args: ['foo:hello']);
+    process.stdout.expect("Precompiling executables...");
+    process.stdout.expect(consumeThrough("hello!"));
+    process.shouldExit();
+    d.dir(
+        p.join(appPath, '.pub', 'bin'),
+        [
+            d.file('sdk-version', '0.1.2+3'),
+            d.dir(
+                'foo',
+                [d.matcherFile('hello.dart.snapshot', contains('hello!'))])]).create();
+  });
+}