Split dart:builtin into dart:builtin and dart:io.

tests/standalone/src/SocketExceptionTest.dart

 // Copyright (c) 2011, 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.
 //
 // Tests socket exceptions.
 
+#import("dart:io");
+
 class SocketExceptionTest {
 
   static final PORT = 0;
   static final HOST = "127.0.0.1";
 
   static void serverSocketExceptionTest() {
     bool exceptionCaught = false;
     bool wrongExceptionCaught = false;
 
     ServerSocket server = new ServerSocket(HOST, PORT, 10);
@@ skipping 152 matching lines @@
   static void testMain() {
     serverSocketExceptionTest();
     clientSocketExceptionTest();
     indexOutOfRangeExceptionTest();
   }
 }
 
 main() {
   SocketExceptionTest.testMain();
 }