RingBuffer<T, N> utility with unit test; use for GC history.

runtime/vm/ring_buffer_test.cc

Index: runtime/vm/ring_buffer_test.cc
===================================================================
--- runtime/vm/ring_buffer_test.cc	(revision 0)
+++ runtime/vm/ring_buffer_test.cc	(revision 0)
@@ -0,0 +1,27 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include "platform/assert.h"
+#include "vm/ring_buffer.h"
+#include "vm/unit_test.h"
+
+namespace dart {
+
+TEST_CASE(RingBuffer) {
+  RingBuffer<int, 2> buf;
+  EXPECT_EQ(0, buf.Size());
+  buf.Add(42);
+  EXPECT_EQ(1, buf.Size());
+  EXPECT_EQ(42, buf.Get(0));
+  buf.Add(87);
+  EXPECT_EQ(2, buf.Size());
+  EXPECT_EQ(87, buf.Get(0));
+  EXPECT_EQ(42, buf.Get(1));
+  buf.Add(-1);
+  EXPECT_EQ(2, buf.Size());
+  EXPECT_EQ(-1, buf.Get(0));
+  EXPECT_EQ(87, buf.Get(1));
+}
+
+}  // namespace dart