pkg/matcher: add isNaN and isNotNaN matchers

pkg/matcher/lib/src/core_matchers.dart

Index: pkg/matcher/lib/src/core_matchers.dart
diff --git a/pkg/matcher/lib/src/core_matchers.dart b/pkg/matcher/lib/src/core_matchers.dart
index cb76d6843de7ee97f4ba1df16964a777ec6c707b..f1a724a72719a7ea4839439bd492a86cda64238f 100644
--- a/pkg/matcher/lib/src/core_matchers.dart
+++ b/pkg/matcher/lib/src/core_matchers.dart
@@ -64,6 +64,24 @@ class _IsFalse extends Matcher {
   Description describe(Description description) => description.add('false');
 }
 
+/// A matcher that matches the numeric value NaN.
+const Matcher isNaN = const _IsNaN();
+
+/// A matcher that matches any non-NaN value.
+const Matcher isNotNaN = const _IsNotNaN();
+
+class _IsNaN extends Matcher {
+  const _IsNaN();
+  bool matches(item, Map matchState) => double.NAN.compareTo(item) == 0;
+  Description describe(Description description) => description.add('NaN');
+}
+
+class _IsNotNaN extends Matcher {
+  const _IsNotNaN();
+  bool matches(item, Map matchState) => double.NAN.compareTo(item) != 0;
+  Description describe(Description description) => description.add('not NaN');
+}
+
 /// Returns a matches that matches if the value is the same instance
 /// as [expected], using [identical].
 Matcher same(expected) => new _IsSameAs(expected);