Fix pub.

sdk/lib/_internal/pub/lib/src/entrypoint.dart

Index: sdk/lib/_internal/pub/lib/src/entrypoint.dart
diff --git a/sdk/lib/_internal/pub/lib/src/entrypoint.dart b/sdk/lib/_internal/pub/lib/src/entrypoint.dart
index 40e2bf7440e6936108ff09d0a27edb8b2c80094d..c866d60eab116e4c1180de96b1750a7bb27c732b 100644
--- a/sdk/lib/_internal/pub/lib/src/entrypoint.dart
+++ b/sdk/lib/_internal/pub/lib/src/entrypoint.dart
@@ -236,9 +236,9 @@ class Entrypoint {
 
   /// Saves a list of concrete package versions to the `pubspec.lock` file.
   void _saveLockFile(List<PackageId> packageIds) {
-    var lockFile = new LockFile(packageIds);
+    _lockFile = new LockFile(packageIds);
     var lockFilePath = path.join(root.dir, 'pubspec.lock');
-    writeTextFile(lockFilePath, lockFile.serialize(root.dir, cache.sources));
+    writeTextFile(lockFilePath, _lockFile.serialize(root.dir, cache.sources));
   }
 
   /// Creates a self-referential symlink in the `packages` directory that allows