Move a number of packages and some of pub over to using source_span.

pkg/string_scanner/test/span_scanner_test.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 string_scanner.span_scanner_test;
 
 import 'package:string_scanner/string_scanner.dart';
 import 'package:unittest/unittest.dart';
 
 void main() {
   var scanner;
   setUp(() {
-    scanner = new SpanScanner('foo\nbar\nbaz', 'source');
+    scanner = new SpanScanner('foo\nbar\nbaz', sourceUrl: 'source');
   });
 
   test("tracks the span for the last match", () {
     scanner.scan('fo');
     scanner.scan('o\nba');
 
     var span = scanner.lastSpan;
     expect(span.start.offset, equals(2));
     expect(span.start.line, equals(0));
     expect(span.start.column, equals(2));
-    expect(span.start.sourceUrl, equals('source'));
+    expect(span.start.sourceUrl, equals(Uri.parse('source')));
 
     expect(span.end.offset, equals(6));
     expect(span.end.line, equals(1));
     expect(span.end.column, equals(2));
-    expect(span.start.sourceUrl, equals('source'));
+    expect(span.start.sourceUrl, equals(Uri.parse('source')));
 
     expect(span.text, equals('o\nba'));
   });
 
   test(".spanFrom() returns a span from a previous state", () {
     scanner.scan('fo');
     var state = scanner.state;
     scanner.scan('o\nba');
     scanner.scan('r\nba');
 
     var span = scanner.spanFrom(state);
     expect(span.text, equals('o\nbar\nba'));
   });
 
   test(".emptySpan returns an empty span at the current location", () {
     scanner.scan('foo\nba');
 
     var span = scanner.emptySpan;
     expect(span.start.offset, equals(6));
     expect(span.start.line, equals(1));
     expect(span.start.column, equals(2));
-    expect(span.start.sourceUrl, equals('source'));
+    expect(span.start.sourceUrl, equals(Uri.parse('source')));
 
     expect(span.end.offset, equals(6));
     expect(span.end.line, equals(1));
     expect(span.end.column, equals(2));
-    expect(span.start.sourceUrl, equals('source'));
+    expect(span.start.sourceUrl, equals(Uri.parse('source')));
 
     expect(span.text, equals(''));
   });
 }