Extract out a source_span package from source_maps.

pkg/source_span/test/utils_test.dart

 // Copyright (c) 2013, 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 for the binary search utility algorithm.
-library test.utils_test;
-
 import 'package:unittest/unittest.dart';
-import 'package:source_maps/src/utils.dart';
+import 'package:source_span/src/utils.dart';
 
 main() {
   group('binary search', () {
     test('empty', () {
       expect(binarySearch([], (x) => true), -1);
     });
 
     test('single element', () {
       expect(binarySearch([1], (x) => true), 0);
       expect(binarySearch([1], (x) => false), 1);
@@ skipping 25 matching lines @@
 }
 
 _linearSearch(list, predicate) {
   if (list.length == 0) return -1;
   for (int i = 0; i < list.length; i++) {
     if (predicate(list[i])) return i;
   }
   return list.length;
 }