[ios] Style cleanups in tab switcher code.

ios/chrome/browser/ui/tab_switcher/tab_switcher_controller.mm

Index: ios/chrome/browser/ui/tab_switcher/tab_switcher_controller.mm
diff --git a/ios/chrome/browser/ui/tab_switcher/tab_switcher_controller.mm b/ios/chrome/browser/ui/tab_switcher/tab_switcher_controller.mm
index 6fb47212d832b8ef2bf2c3d8be957786a0c7ed75..92e76d1c9811eb9af4bb3c35aeff72cfea730962 100644
--- a/ios/chrome/browser/ui/tab_switcher/tab_switcher_controller.mm
+++ b/ios/chrome/browser/ui/tab_switcher/tab_switcher_controller.mm
@@ -1003,11 +1003,16 @@ enum class SnapshotViewOption {
 }
 
 - (void)localSessionMayNeedUpdate:(TabSwitcherSessionType)type {
-  if (type == TabSwitcherSessionType::REGULAR_SESSION) {
-    [_onTheRecordSession updateCollectionViewIfNeeded];
-  } else {
-    DCHECK(type == TabSwitcherSessionType::OFF_THE_RECORD_SESSION);
-    [_offTheRecordSession updateCollectionViewIfNeeded];
+  switch (type) {
+    case TabSwitcherSessionType::REGULAR_SESSION:
+      [_onTheRecordSession updateCollectionViewIfNeeded];
+      break;
+    case TabSwitcherSessionType::OFF_THE_RECORD_SESSION:
+      [_offTheRecordSession updateCollectionViewIfNeeded];
+      break;
+    case TabSwitcherSessionType::DISTANT_SESSION:
+      NOTREACHED();
+      break;
   }
 }