Add support for Expect.equals in the Leg core library.

frog/leg/lib/core.dart

Index: frog/leg/lib/core.dart
diff --git a/frog/leg/lib/core.dart b/frog/leg/lib/core.dart
index 5712d6b25c3ffd21167766411f512cbcec13c7f2..47cb7bf922858fedba9d810a95c9d0406c9da382 100644
--- a/frog/leg/lib/core.dart
+++ b/frog/leg/lib/core.dart
@@ -249,6 +249,15 @@ class bool {}
 class Object {}
 class List<T> {}
 
+class Expect {
+  static void equals(var expected, var actual) {
+    if (expected == actual) return;
+    print('Expect.equals(expected: <' + expected.toString() +
+          '>, actual:<' + actual.toString() + '> fails.');
+    throw 'Expect.equals failed.';
+  }
+}
+
 class Stopwatch {
   double startMs;
   double elapsedMs;