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

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

+library pub_tests;
+import 'package:path/path.dart' as p;
+import 'package:scheduled_test/scheduled_test.dart';
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+main() {
+  initConfig();
+  integration(
+      "doesn't recreate a snapshot when no dependencies of a package " "have changed",
+      () {
+    servePackages((builder) {
+      builder.serve("foo", "1.2.3", deps: {
+        "bar": "any"
+      },
+          contents: [
+              d.dir("bin", [d.file("hello.dart", "void main() => print('hello!');")])]);
+      builder.serve("bar", "1.2.3");
+    });
+    d.appDir({
+      "foo": "1.2.3"
+    }).create();
+    pubGet(output: contains("Precompiled foo:hello."));
+    pubUpgrade(output: isNot(contains("Precompiled foo:hello.")));
+    d.dir(
+        p.join(appPath, '.pub', 'bin'),
+        [
+            d.file('sdk-version', '0.1.2+3\n'),
+            d.dir(
+                'foo',
+                [d.matcherFile('hello.dart.snapshot', contains('hello!'))])]).validate();
+  });
+}