Cleanup 1: split parts into their own libraries, remove unused imports

pkg/compiler/lib/src/native/scanner.dart

Index: pkg/compiler/lib/src/native/scanner.dart
diff --git a/pkg/compiler/lib/src/native/scanner.dart b/pkg/compiler/lib/src/native/scanner.dart
index c18bfa8ef48b99d28efeea4848d9f8c298e31516..c54b937244b82112974b5e1a91ba97944e3d95f9 100644
--- a/pkg/compiler/lib/src/native/scanner.dart
+++ b/pkg/compiler/lib/src/native/scanner.dart
@@ -2,7 +2,17 @@
 // 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.
 
-part of native;
+import '../common.dart';
+import '../parser/listener.dart' show
+    Listener;
+import '../parser/element_listener.dart' show
+    ElementListener;
+import '../tokens/token.dart' show
+    BeginGroupToken,
+    Token;
+import '../tokens/token_constants.dart' as Tokens show
+    EOF_TOKEN,
+    STRING_TOKEN;
 
 void checkAllowedLibrary(ElementListener listener, Token token) {
   if (listener.scannerOptions.canUseNative) return;