Add CSS Animations performance tests

tools/perf/page_sets/tough_animation_cases/resources/animation.css

Index: tools/perf/page_sets/tough_animation_cases/resources/animation.css
diff --git a/tools/perf/page_sets/tough_animation_cases/resources/animation.css b/tools/perf/page_sets/tough_animation_cases/resources/animation.css
new file mode 100644
index 0000000000000000000000000000000000000000..2ee2ed5c612d2d7473ab6db473a24b5ef562a22d
--- /dev/null
+++ b/tools/perf/page_sets/tough_animation_cases/resources/animation.css
@@ -0,0 +1,19 @@
+/* Copyright 2014 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+target {
+  -webkit-animation: anim 1s linear;
+}
+target.reverse {
+  -webkit-animation: reverse-anim 1s linear;
+}
+@-webkit-keyframes anim {
+  0% { opacity: 0; }
+  100% { opacity: 1; }
+}
+@-webkit-keyframes reverse-anim {
+  0% { opacity: 1; }
+  100% { opacity: 0; }
+}