Adds AnimationContainer, which can be used to group a set of

app/throb_animation.cc

Index: app/throb_animation.cc
diff --git a/app/throb_animation.cc b/app/throb_animation.cc
index 28b5763daa655a1bb8e0f85bd1bf1a7d069b0ea4..e8e57303ba899d3d6972d4bf2070e4bf695f5fa2 100644
--- a/app/throb_animation.cc
+++ b/app/throb_animation.cc
@@ -43,8 +43,9 @@ void ThrobAnimation::Hide() {
   SlideAnimation::Hide();
 }
 
-void ThrobAnimation::Step() {
-  Animation::Step();
+void ThrobAnimation::Step(base::TimeTicks time_now) {
+  Animation::Step(time_now);
+
   if (!IsAnimating() && throbbing_) {
     // Were throbbing a finished a cycle. Start the next cycle unless we're at
     // the end of the cycles, in which case we stop.