Comment improvements

pkg/front_end/test/scanner_test.dart

 // Copyright (c) 2016, 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:front_end/src/base/errors.dart';
 import 'package:front_end/src/base/jenkins_smi_hash.dart';
 import 'package:front_end/src/scanner/errors.dart';
 import 'package:front_end/src/scanner/reader.dart';
 import 'package:front_end/src/scanner/scanner.dart';
 import 'package:front_end/src/scanner/token.dart';
@@ skipping 765 matching lines @@
     var openParen = _scan('([)') as BeginToken;
     var openBracket = openParen.next as BeginToken;
     var closeParen = openBracket.next;
     expect(closeParen.next.type, TokenType.EOF);
     expect(openParen.endToken, isNull);
     expect(openBracket.endToken, isNull);
   }
 
   void test_mismatched_opener_in_interpolation() {
     // In an interpolation expression, analyzer considers a closing `}` to
-    // always matche the preceding unmatched `{`, even if there are intervening
+    // always match the preceding unmatched `{`, even if there are intervening
     // unmatched tokens, which means that `"${({(}}"` parses as though the open
     // parens are unmatched but everything else is matched.
     var stringStart = _scan(r'"${({(}}"');
     var interpolationStart = stringStart.next as BeginToken;
     var openParen1 = interpolationStart.next as BeginToken;
     var openBrace = openParen1.next as BeginToken;
     var openParen2 = openBrace.next as BeginToken;
     var closeBrace = openParen2.next;
     var interpolationEnd = closeBrace.next;
     var stringEnd = interpolationEnd.next;
@@ skipping 715 matching lines @@
   _TestScanner(CharacterReader reader, [this.listener]) : super(reader);
 
   @override
   void reportError(
       ScannerErrorCode errorCode, int offset, List<Object> arguments) {
     if (listener != null) {
       listener.errors.add(new TestError(offset, errorCode, arguments));
     }
   }
 }