pkg/matcher: add isNaN and isNotNaN matchers

pkg/matcher/test/core_matchers_test.dart

Index: pkg/matcher/test/core_matchers_test.dart
diff --git a/pkg/matcher/test/core_matchers_test.dart b/pkg/matcher/test/core_matchers_test.dart
index 7e9b246d0cd4f231e3881c9884bb997a767151b6..44545780416863ace08e2f8c22d4dbd97e183fb4 100644
--- a/pkg/matcher/test/core_matchers_test.dart
+++ b/pkg/matcher/test/core_matchers_test.dart
@@ -33,6 +33,16 @@ void main() {
     shouldFail(null, isNotNull, "Expected: not null Actual: <null>");
   });
 
+  test('isNaN', () {
+    shouldPass(double.NaN, isNaN);
+    shouldFail(3.1, isNaN, "Expected: NaN Actual: <3.1>");
+  });
+
+  test('isNotNaN', () {
+    shouldPass(3.1, isNotNaN);
+    shouldFail(NaN, isNotNaN, "Expected: not NaN Actual: <NaN>");
+  });
+
   test('same', () {
     var a = new Map();
     var b = new Map();