Make the universe parts into small libraries.

tests/compiler/dart2js/semantic_visitor_test.dart

Index: tests/compiler/dart2js/semantic_visitor_test.dart
diff --git a/tests/compiler/dart2js/semantic_visitor_test.dart b/tests/compiler/dart2js/semantic_visitor_test.dart
index 575b758cecc5d9c0e1edbd836952de7dd837eb20..103cdc84cb12e8154db2f642e0b4c3a2bee04a44 100644
--- a/tests/compiler/dart2js/semantic_visitor_test.dart
+++ b/tests/compiler/dart2js/semantic_visitor_test.dart
@@ -19,8 +19,9 @@ import 'package:compiler/src/resolution/operators.dart';
 import 'package:compiler/src/resolution/semantic_visitor.dart';
 import 'package:compiler/src/resolution/tree_elements.dart';
 import 'package:compiler/src/tree/tree.dart';
-import 'package:compiler/src/universe/universe.dart' show
-    CallStructure,
+import 'package:compiler/src/universe/call_structure.dart' show
+    CallStructure;
+import 'package:compiler/src/universe/selector.dart' show
     Selector;
 import 'memory_compiler.dart';