Add support for pub install.

utils/pub/command_list.dart

Index: utils/pub/command_list.dart
diff --git a/utils/pub/command_list.dart b/utils/pub/command_list.dart
index 8a45cfcd72d6ecd22730d47da956a82317fdc66b..138037667b48b69f23ec4435facb738c42f355d5 100644
--- a/utils/pub/command_list.dart
+++ b/utils/pub/command_list.dart
@@ -12,11 +12,23 @@ class ListCommand extends PubCommand {
   String get description() => 'print the contents of repositories';
 
   void onRun() {
-    cache.listAll().then((packages) {
-      packages.sort((a, b) => a.name.compareTo(b.name));
-      for (final package in packages) {
-        print(package.name);
+    printIds(String title, List<PackageId> ids) {
+      ids = new List<PackageId>.from(ids);
+      ids.sort((a, b) {
+        var sourceComp = a.source.name.compareTo(b.source.name);
+        if (sourceComp != 0) return sourceComp;
+        return a.name.compareTo(b.name);
+      });
+
+      print('From $title:');
+      for (var id in ids) {
+        print('  $id');
       }
-    });
+    }
+
+    // TODO(nweiz): also list the contents of the application cache when it's
+    // able to determine the source of its packages (that is, when we have a
+    // lockfile).
+    systemCache.listAll().then((ids) => printIds('system cache', ids));
   }
 }