Create an apptesting framework for dart.

third_party/dart-packages/matcher/matcher/src/core_matchers.dart

Index: third_party/dart-packages/matcher/matcher/src/core_matchers.dart
diff --git a/sky/tests/resources/third_party/matcher/src/core_matchers.dart b/third_party/dart-packages/matcher/matcher/src/core_matchers.dart
similarity index 99%
copy from sky/tests/resources/third_party/matcher/src/core_matchers.dart
copy to third_party/dart-packages/matcher/matcher/src/core_matchers.dart
index abecb769856fa31f053c2a0202c904948d5f30e9..a3d1f5750dcfeea6736b26a4b8073a82ee31de0a 100644
--- a/sky/tests/resources/third_party/matcher/src/core_matchers.dart
+++ b/third_party/dart-packages/matcher/matcher/src/core_matchers.dart
@@ -297,8 +297,8 @@ class _StringEqualsMatcher extends Matcher {
     } else {
       var buff = new StringBuffer();
       buff.write('is different.');
-      var escapedItem = _escape(item);
-      var escapedValue = _escape(_value);
+      var escapedItem = escape(item);
+      var escapedValue = escape(_value);
       int minLength = escapedItem.length < escapedValue.length
           ? escapedItem.length
           : escapedValue.length;
@@ -334,9 +334,6 @@ class _StringEqualsMatcher extends Matcher {
     }
   }
 
-  static String _escape(String s) =>
-      s.replaceAll('\n', '\\n').replaceAll('\r', '\\r').replaceAll('\t', '\\t');
-
   static void _writeLeading(StringBuffer buff, String s, int start) {
     if (start > 10) {
       buff.write('... ');