Provide a way to insert multiple overlays at once.

packages/flutter/lib/src/widgets/overlay.dart

@@ -66,6 +66,18 @@ class OverlayState extends State<Overlay> {
     });
   }
 
+  void insertAll(Iterable<OverlayEntry> entries, { OverlayEntry above }) {
+    assert(above == null || (above._state == this && _entries.contains(above)));
+    for (OverlayEntry entry in entries) {
+      assert(entry._state == null);
+      entry._state = this;
+    }
+    setState(() {
+      int index = above == null ? _entries.length : _entries.indexOf(above) + 1;
+      _entries.insertAll(index, entries);
+    });
+  }
+
   void _remove(OverlayEntry entry) {
     setState(() {
       _entries.remove(entry);

packages/flutter/lib/src/widgets/routes.dart

@@ -41,11 +41,9 @@ abstract class OverlayRoute<T> extends Route<T> {
   final List<OverlayEntry> _overlayEntries = <OverlayEntry>[];
 
   void didPush(OverlayState overlay, OverlayEntry insertionPoint) {
-    for (WidgetBuilder builder in builders) {
+    for (WidgetBuilder builder in builders)
       _overlayEntries.add(new OverlayEntry(builder: builder));
-      overlay?.insert(_overlayEntries.last, above: insertionPoint);
-      insertionPoint = _overlayEntries.last;
-    }
+    overlay?.insertAll(_overlayEntries, above: insertionPoint);
   }
 
   // Subclasses shouldn't call this if they want to delay the finished() call.