make overflow dots on iOS horizontal in gallery (#20702)

diff --git a/examples/flutter_gallery/lib/demo/material/bottom_app_bar_demo.dart b/examples/flutter_gallery/lib/demo/material/bottom_app_bar_demo.dart
index 82eddf0..d3d9576 100644
--- a/examples/flutter_gallery/lib/demo/material/bottom_app_bar_demo.dart
+++ b/examples/flutter_gallery/lib/demo/material/bottom_app_bar_demo.dart
@@ -372,7 +372,11 @@
         },
       ),
       new IconButton(
-        icon: const Icon(Icons.more_vert),
+        icon: new Icon(
+          Theme.of(context).platform == TargetPlatform.iOS
+              ? Icons.more_horiz
+              : Icons.more_vert,
+        ),
         onPressed: () {
           Scaffold.of(context).showSnackBar(
             const SnackBar(content: Text('This is a dummy menu action.')),
diff --git a/examples/flutter_gallery/lib/demo/material/list_demo.dart b/examples/flutter_gallery/lib/demo/material/list_demo.dart
index fb4fe0e..ab5baf7 100644
--- a/examples/flutter_gallery/lib/demo/material/list_demo.dart
+++ b/examples/flutter_gallery/lib/demo/material/list_demo.dart
@@ -227,7 +227,11 @@
             },
           ),
           new IconButton(
-            icon: const Icon(Icons.more_vert),
+            icon: new Icon(
+              Theme.of(context).platform == TargetPlatform.iOS
+                  ? Icons.more_horiz
+                  : Icons.more_vert,
+            ),
             tooltip: 'Show menu',
             onPressed: _bottomSheet == null ? _showConfigurationSheet : null,
           ),
diff --git a/examples/flutter_gallery/lib/demo/material/reorderable_list_demo.dart b/examples/flutter_gallery/lib/demo/material/reorderable_list_demo.dart
index 3f778ba..6762e54 100644
--- a/examples/flutter_gallery/lib/demo/material/reorderable_list_demo.dart
+++ b/examples/flutter_gallery/lib/demo/material/reorderable_list_demo.dart
@@ -168,7 +168,11 @@
             },
           ),
           new IconButton(
-            icon: const Icon(Icons.more_vert),
+            icon: new Icon(
+              Theme.of(context).platform == TargetPlatform.iOS
+                  ? Icons.more_horiz
+                  : Icons.more_vert,
+            ),
             tooltip: 'Show menu',
             onPressed: _bottomSheet == null ? _showConfigurationSheet : null,
           ),
diff --git a/examples/flutter_gallery/lib/demo/material/search_demo.dart b/examples/flutter_gallery/lib/demo/material/search_demo.dart
index 09c24be..8873abb 100644
--- a/examples/flutter_gallery/lib/demo/material/search_demo.dart
+++ b/examples/flutter_gallery/lib/demo/material/search_demo.dart
@@ -52,7 +52,11 @@
           ),
           new IconButton(
             tooltip: 'More (not implemented)',
-            icon: const Icon(Icons.more_vert),
+            icon: new Icon(
+              Theme.of(context).platform == TargetPlatform.iOS
+                  ? Icons.more_horiz
+                  : Icons.more_vert,
+            ),
             onPressed: () {},
           ),
         ],