Install before starting the server if the lockfile is out of date.

sdk/lib/_internal/pub/test/serve/installs_first_if_dependency_added_test.dart

Index: sdk/lib/_internal/pub/test/serve/installs_first_if_dependency_added_test.dart
diff --git a/sdk/lib/_internal/pub/test/serve/missing_dependency_file_test.dart b/sdk/lib/_internal/pub/test/serve/installs_first_if_dependency_added_test.dart
similarity index 57%
copy from sdk/lib/_internal/pub/test/serve/missing_dependency_file_test.dart
copy to sdk/lib/_internal/pub/test/serve/installs_first_if_dependency_added_test.dart
index d1c47f24e8946cccca4545d3669afe06b403fde3..42bcdfd91bb7dc8e06f9c7c698c17f8d552c99a3 100644
--- a/sdk/lib/_internal/pub/test/serve/missing_dependency_file_test.dart
+++ b/sdk/lib/_internal/pub/test/serve/installs_first_if_dependency_added_test.dart
@@ -5,6 +5,7 @@
 library pub_tests;
 
 import 'dart:io';
+import 'dart:json' as json;
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
@@ -12,23 +13,27 @@ import 'utils.dart';
 
 main() {
   initConfig();
-  integration("responds with a 404 for a missing files in dependencies", () {
+  integration("installs first if a dependency is not in the lock file", () {
     d.dir("foo", [
-      d.libPubspec("foo", "0.0.1")
+      d.libPubspec("foo", "0.0.1"),
+      d.libDir("foo")
     ]).create();
 
+    // Create a lock file without "foo".
+    d.dir(appPath, [
+      d.appPubspec()
+    ]).create();
+    pubInstall();
+
+    // Add it to the pubspec.
     d.dir(appPath, [
       d.appPubspec({
         "foo": {"path": "../foo"}
       })
     ]).create();
 
-    pubInstall();
-    startPubServe();
-    requestShould404("packages/foo/nope.dart");
-    requestShould404("assets/foo/nope.png");
-    requestShould404("dir/packages/foo/nope.dart");
-    requestShould404("dir/assets/foo/nope.png");
+    startPubServe(shouldInstallFirst: true);
+    requestShouldSucceed("packages/foo/foo.dart", 'main() => "foo";');
     endPubServe();
   });
 }