Fix app launcher animation tearing on OSX Mavericks.

ui/app_list/cocoa/app_list_view_controller.mm

Index: ui/app_list/cocoa/app_list_view_controller.mm
diff --git a/ui/app_list/cocoa/app_list_view_controller.mm b/ui/app_list/cocoa/app_list_view_controller.mm
index a28171cd7e3ef41f0e1d73997a171342b2241a9c..3d9b16734d0af366d55514d00821a8f4d393877a 100644
--- a/ui/app_list/cocoa/app_list_view_controller.mm
+++ b/ui/app_list/cocoa/app_list_view_controller.mm
@@ -197,6 +197,12 @@ void AppListModelObserverBridge::OnProfilesChanged() {
           [AppsGridController scrollerPadding]);
 
   contentsView_.reset([[FlippedView alloc] initWithFrame:contentsRect]);
+
+  // The contents view contains animations both from an NSCollectionView and the
+  // app list's own transitive drag layers. Ensure the subviews have access to
+  // a compositing layer they can share.
+  [contentsView_ setWantsLayer:YES];
+
   backgroundView_.reset(
       [[BackgroundView alloc] initWithFrame:
               NSMakeRect(0, 0, NSMaxX(contentsRect), NSMaxY(contentsRect))]);