pkg/unittest: Moved `fail` to matcher library

pkg/unittest/lib/src/expect.dart

Index: pkg/unittest/lib/src/expect.dart
diff --git a/pkg/unittest/lib/src/expect.dart b/pkg/unittest/lib/src/expect.dart
index 49561476f038aa1d8973899e279f7a879ed64920..c1e2f47334bf35c8374eb5f9273cd0c920d6a733 100644
--- a/pkg/unittest/lib/src/expect.dart
+++ b/pkg/unittest/lib/src/expect.dart
@@ -68,6 +68,13 @@ void expect(actual, matcher, {String reason, FailureHandler failureHandler,
   }
 }
 
+void fail(String message, {FailureHandler failureHandler}) {
+  if (failureHandler == null) {
+    failureHandler = getOrCreateExpectFailureHandler();
+  }
+  failureHandler.fail(message);
+}
+
 /**
  * Takes an argument and returns an equivalent matcher.
  * If the argument is already a matcher this does nothing,