Remove use of deprecated mirror API from pkg/unittest.

pkg/unittest/lib/mirror_matchers.dart

Index: pkg/unittest/lib/mirror_matchers.dart
diff --git a/pkg/unittest/lib/mirror_matchers.dart b/pkg/unittest/lib/mirror_matchers.dart
index 7d1597f2ac27f59c752109141a93a6a58ce6c51c..25f2b6d69206d80b4b77bedadd1901eafd634b09 100644
--- a/pkg/unittest/lib/mirror_matchers.dart
+++ b/pkg/unittest/lib/mirror_matchers.dart
@@ -49,10 +49,19 @@ class _HasProperty extends Matcher {
     var mirror = reflect(item);
     var classMirror = mirror.type;
     var symbol = new Symbol(_name);
-    if (!classMirror.getters.containsKey(symbol)) {
+    var candidate = classMirror.declarations[symbol];
+    if (candidate == null) {
       addStateInfo(matchState, {'reason': 'has no property named "$_name"'});
       return false;
     }
+    bool isInstanceField = candidate is VariableMirror && !candidate.isStatic;
+    bool isInstanceGetter =
+        candidate is MethodMirror && candidate.isGetter && !candidate.isStatic;
+    if (!(isInstanceField || isInstanceGetter)) {
+      addStateInfo(matchState, {'reason':
+          'has a member named "$_name", but it is not an instance property'});
+      return false;
+    }
     if (_matcher == null) return true;
     var result = mirror.getField(symbol);
     var resultMatches = _matcher.matches(result.reflectee, matchState);