Move dart2jslib parts into separate libraries.

pkg/compiler/lib/src/js_backend/codegen/codegen.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library code_generator;
 
 import 'glue.dart';
 
 import '../../tree_ir/tree_ir_nodes.dart' as tree_ir;
 import '../../tree_ir/tree_ir_nodes.dart' show BuiltinOperator;
 import '../../js/js.dart' as js;
 import '../../elements/elements.dart';
 import '../../io/source_information.dart' show SourceInformation;
 import '../../util/maplet.dart';
 import '../../constants/values.dart';
 import '../../dart2jslib.dart';
 import '../../dart_types.dart';
 import '../../types/types.dart' show TypeMask;
-import '../../universe/universe.dart' show UniverseSelector;
+import '../../universe/universe.dart' show
+    Selector,
+    UniverseSelector;
+import '../../util/util.dart' show CURRENT_ELEMENT_SPANNABLE;
 import '../../closure.dart' show ClosureClassElement;
 
 class CodegenBailout {
   final tree_ir.Node node;
   final String reason;
   CodegenBailout(this.node, this.reason);
   String get message {
     return 'bailout${node != null ? " on $node" : ""}: $reason';
   }
 }
@@ skipping 803 matching lines @@
   js.Expression visitAwait(tree_ir.Await node) {
     return new js.Await(visitExpression(node.input));
   }
 
   visitFunctionExpression(tree_ir.FunctionExpression node) {
     // FunctionExpressions are currently unused.
     // We might need them if we want to emit raw JS nested functions.
     throw 'FunctionExpressions should not be used';
   }
 }