Refactor Source to take the system cache as a parameter.

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 c022af7d365085a03f18826bbdd532f5821bc903..3c5bb7b48c67de6befb1d4e5fa47f15491b1b67a 100644
--- a/utils/pub/system_cache.dart
+++ b/utils/pub/system_cache.dart
@@ -6,6 +6,7 @@
 
 #import('io.dart');
 #import('package.dart');
+#import('source.dart');
 #import('source_registry.dart');
 #import('utils.dart');
 
@@ -40,6 +41,15 @@ class SystemCache {
     sources = new SourceRegistry();
 
   /**
+   * Registers a new source. This source may not have the same name as a source

[Bob Nystrom, 2012/07/10 16:12:36]

"may" -> "must"

[nweiz, 2012/07/10 18:13:01]

Done.

+   * that's already been registered.
+   */
+  void register(Source source) {
+    source.bind(this);
+    sources.register(source);
+  }
+
+  /**
    * Loads all of the package ids in the cache and returns them.
    */
   Future<List<PackageId>> listAll() {
@@ -72,8 +82,7 @@ class SystemCache {
     var pending = _pendingInstalls[id];
     if (pending != null) return pending;
 
-    var sourceDir = join(rootDir, id.source.name);
-    var path = id.source.systemCacheDirectory(id, sourceDir);
+    var path = id.source.systemCacheDirectory(id);
     var future = exists(path).chain((exists) {
       // TODO(nweiz): better error handling
       if (exists) throw 'Package $id is already installed.';