Source selection API abstraction first cut.

pkg/analyzer_experimental/test/services/formatter_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.
 
 import 'package:unittest/unittest.dart';
 
 import 'package:analyzer_experimental/src/generated/scanner.dart';
 import 'package:analyzer_experimental/src/services/formatter_impl.dart';
 import 'package:analyzer_experimental/src/services/writer.dart';
 
@@ skipping 749 matching lines @@
         '}',
         'for (final foo in bar.foos) {\n'
         '  print(foo);\n'
         '}'
       );
     });
 
     test('initialIndent', () {
       var formatter = new CodeFormatter(
           new FormatterOptions(initialIndentationLevel: 2));
-      var formattedSource = formatter.format(CodeKind.STATEMENT, 'var x;');
+      var formattedSource = 
+          formatter.format(CodeKind.STATEMENT, 'var x;').source;
       expect(formattedSource, startsWith('    '));
     });
 
   });
 
 
   /// Token streams
   group('token streams', () {
 
     test('string tokens', () {
@@ skipping 167 matching lines @@
     new StringToken(TokenType.CLOSE_PAREN, '}', offset);
 
 Token chain(List<Token> tokens) {
   for (var i = 0; i < tokens.length - 1; ++i) {
     tokens[i].setNext(tokens[i + 1]);
   }
   return tokens[0];
 }
 
 String formatCU(src, {options: const FormatterOptions()}) =>
-    new CodeFormatter(options).format(CodeKind.COMPILATION_UNIT, src);
+    new CodeFormatter(options).format(CodeKind.COMPILATION_UNIT, src).source;
 
 String formatStatement(src, {options: const FormatterOptions()}) =>
-    new CodeFormatter(options).format(CodeKind.STATEMENT, src);
+    new CodeFormatter(options).format(CodeKind.STATEMENT, src).source;
 
 Token tokenize(String str) => new StringScanner(null, str, null).tokenize();
 
 
 expectTokenizedEqual(String s1, String s2) =>
     expectStreamsEqual(tokenize(s1), tokenize(s2));
 
 expectTokenizedNotEqual(String s1, String s2) =>
     expect(()=> expectStreamsEqual(tokenize(s1), tokenize(s2)),
     throwsA(new isInstanceOf<FormatterException>()));
 
 expectStreamsEqual(Token t1, Token t2) =>
     new TokenStreamComparator(null, t1, t2).verifyEquals();
 
 expectStreamsNotEqual(Token t1, Token t2) =>
     expect(() => new TokenStreamComparator(null, t1, t2).verifyEquals(),
     throwsA(new isInstanceOf<FormatterException>()));
 
 expectCUFormatsTo(src, expected) => expect(formatCU(src), equals(expected));
 
 expectStmtFormatsTo(src, expected) => expect(formatStatement(src),
     equals(expected));