Merge pull request #146 from cbracken/deprecate-system-clock

Remove SYSTEM_CLOCK. Use const Clock() instead.
diff --git a/lib/clock.dart b/lib/clock.dart
index f3327f7..ddef5a7 100644
--- a/lib/clock.dart
+++ b/lib/clock.dart
@@ -20,9 +20,6 @@
 /// Return current system time.
 DateTime systemTime() => new DateTime.now();
 
-/// A predefined instance of [Clock] that's based on system clock.
-const SYSTEM_CLOCK = const Clock();
-
 /// Days in a month. This array uses 1-based month numbers, i.e. January is
 /// the 1-st element in the array, not the 0-th.
 const _DAYS_IN_MONTH =
diff --git a/test/clock_test.dart b/test/clock_test.dart
index 73cdeb4..09ea399 100644
--- a/test/clock_test.dart
+++ b/test/clock_test.dart
@@ -32,8 +32,7 @@
     });
 
     test('should return a non-null value from system clock', () {
-      expect(new Clock().now(), isNotNull);
-      expect(SYSTEM_CLOCK.now(), isNotNull);
+      expect(const Clock().now(), isNotNull);
     });
 
     // This test may be flaky on certain systems. I ran it over 10 million
@@ -45,7 +44,7 @@
           new Clock().now()).inMilliseconds.abs(),
               lessThan(epsilon));
       expect(new DateTime.now().difference(
-          SYSTEM_CLOCK.now()).inMilliseconds.abs(),
+          const Clock().now()).inMilliseconds.abs(),
               lessThan(epsilon));
     });