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

pkg/compiler/lib/src/native/scanner.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.
 
-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;
   listener.reportError(token, MessageKind.NATIVE_NOT_SUPPORTED);
 }
 
 Token handleNativeBlockToSkip(Listener listener, Token token) {
   checkAllowedLibrary(listener, token);
   token = token.next;
   if (identical(token.kind, Tokens.STRING_TOKEN)) {
@@ skipping 16 matching lines @@
     hasExpression = true;
     listener.beginLiteralString(token);
     listener.endLiteralString(0);
     token = token.next;
   }
   listener.endReturnStatement(hasExpression, begin, token);
   // TODO(ngeoffray): expect a ';'.
   // Currently there are method with both native marker and Dart body.
   return token.next;
 }