Make ~/, round, ceil, floor, truncate return ints. Remove toInt.

samples/swarm/swarm_ui_lib/layout/GridTracks.dart

Index: samples/swarm/swarm_ui_lib/layout/GridTracks.dart
diff --git a/samples/swarm/swarm_ui_lib/layout/GridTracks.dart b/samples/swarm/swarm_ui_lib/layout/GridTracks.dart
index 99d5e7c7d1c2d40e3eed2ac53deb3f3134a5f0ac..122381475d565662ea4ed98b2d40109658cc7bce 100644
--- a/samples/swarm/swarm_ui_lib/layout/GridTracks.dart
+++ b/samples/swarm/swarm_ui_lib/layout/GridTracks.dart
@@ -91,7 +91,7 @@ class GridItemAlignment {
         size = Math.min(size, span.length);
         num center = span.start + span.length / 2;
         num left = center - size / 2;
-        return new _GridLocation(left.round().toInt(), size);
+        return new _GridLocation(left.round(), size);
       case 'stretch':
         return span;
     }