Don't extract the name of a package from its description.

utils/pub/system_cache.dart

Index: utils/pub/system_cache.dart
diff --git a/utils/pub/system_cache.dart b/utils/pub/system_cache.dart
index 24db19de99a9be705a71f6f3d48043af228b7414..de236ac8067996018a1de0b5d924f3036e0baa45 100644
--- a/utils/pub/system_cache.dart
+++ b/utils/pub/system_cache.dart
@@ -61,7 +61,8 @@ class SystemCache {
           // TODO(rnystrom): Once there are cached packages and this path is
           // being used, figure out how version numbers should be acquired.
           return subpaths.map((subpath) =>
-            new PackageId(source, Version.none, basename(subpath)));
+            new PackageId(
+                basename(subpath), source, Version.none, basename(subpath)));
         });
       });
       return Futures.wait(sources).transform(flatten);