Split installing a package locally from symlinking to it.

sdk/lib/_internal/pub/test/lock_file_test.dart

Index: sdk/lib/_internal/pub/test/lock_file_test.dart
diff --git a/sdk/lib/_internal/pub/test/lock_file_test.dart b/sdk/lib/_internal/pub/test/lock_file_test.dart
index 04430ab65e47b6c3d9eb7f1da2b65779d558935a..85724e46ffdff0725973414e5eec90d5fcaccacc 100644
--- a/sdk/lib/_internal/pub/test/lock_file_test.dart
+++ b/sdk/lib/_internal/pub/test/lock_file_test.dart
@@ -23,9 +23,12 @@ class MockSource extends Source {
   Future<Pubspec> doDescribe(PackageId id) => throw new UnsupportedError(
       "Cannot describe mock packages.");
 
-  Future<bool> get(PackageId id, String path) => throw new UnsupportedError(
+  Future ensureLocal(PackageId id) => throw new UnsupportedError(
       "Cannot get a mock package.");
 
+  Future get(PackageId id, String symlink) => throw new UnsupportedError(
+      "Cannot get an mock.");
+
   Future<String> getDirectory(PackageId id) => throw new UnsupportedError(
       "Cannot get the directory for mock packages.");