ui [nfc]: Pull out iconDataForStream helper

Author: sirpengi

lib/widgets/icons.dart

@@ -1,6 +1,8 @@
 
 import 'package:flutter/widgets.dart';
 
+import '../api/model/model.dart';
+
 // ignore_for_file: constant_identifier_names
 
 /// Identifiers for Zulip's custom icons.
@@ -63,3 +65,14 @@ abstract final class ZulipIcons {
 
   // END GENERATED ICON DATA
 }
+
+IconData iconDataForStream(ZulipStream stream) {
+  // TODO: these icons aren't quite right yet;
+  //   see this message and the one after it:
+  //   https://chat.zulip.org/#narrow/stream/243-mobile-team/topic/design.3A.20.23F117.20.22Inbox.22.20screen/near/1680637
+  return switch(stream) {
+    ZulipStream(isWebPublic: true) => ZulipIcons.globe,
+    ZulipStream(inviteOnly: true) => ZulipIcons.lock,
+    ZulipStream() => ZulipIcons.hash_sign,
+  };
+}

lib/widgets/inbox.dart

@@ -385,13 +385,7 @@ class _StreamHeaderItem extends _HeaderItem {
   });
 
   @override get title => subscription.name;
-  @override get icon => switch (subscription) {
-    // TODO these icons aren't quite right yet; see this message and the following:
-    //   https://chat.zulip.org/#narrow/stream/243-mobile-team/topic/design.3A.20.23F117.20.22Inbox.22.20screen/near/1680637
-    Subscription(isWebPublic: true) => ZulipIcons.globe,
-    Subscription(inviteOnly: true) => ZulipIcons.lock,
-    Subscription() => ZulipIcons.hash_sign,
-  };
+  @override get icon => iconDataForStream(subscription);
   @override get collapsedIconColor => subscription.colorSwatch().iconOnPlainBackground;
   @override get uncollapsedIconColor => subscription.colorSwatch().iconOnBarBackground;
   @override get uncollapsedBackgroundColor =>

lib/widgets/message_list.dart

@@ -88,12 +88,8 @@ class MessageListAppBarTitle extends StatelessWidget {
   final Narrow narrow;
 
   Widget _buildStreamRow(ZulipStream? stream, String text) {
-    final icon = switch (stream) {
-      ZulipStream(isWebPublic: true) => ZulipIcons.globe,
-      ZulipStream(inviteOnly: true) => ZulipIcons.lock,
-      ZulipStream() => ZulipIcons.hash_sign,
-      null => null, // A null [Icon.icon] makes a blank space.
-    };
+    // A null [Icon.icon] makes a blank space.
+    final icon = (stream != null) ? iconDataForStream(stream) : null;
     return Row(
       mainAxisSize: MainAxisSize.min,
       // TODO(design): The vertical alignment of the stream privacy icon is a bit ad hoc.