[ios] Style cleanups in tab switcher code.

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_controller.h"
 
 #include "base/ios/block_types.h"
 #include "base/ios/weak_nsobject.h"
 #include "base/mac/scoped_nsobject.h"
 #include "base/metrics/user_metrics.h"
@@ skipping 985 matching lines @@
            .get()) {
     DCHECK([panel isKindOfClass:[TabSwitcherPanelController class]]);
     if ([panel sessionTag] == tag) {
       [panel updateCollectionViewIfNeeded];
       return;
     }
   }
 }
 
 - (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;
   }
 }
 
 - (void)signInPanelChangedTo:(TabSwitcherSignInPanelsType)newPanelType {
   if (_signInPanelType == newPanelType)
     return;
 
   // Remove promo panel that is no longer relevant, if any.
   if (_signInPanelType != TabSwitcherSignInPanelsType::NO_PANEL) {
     _shouldRemovePromoPanelHeaderCell = YES;
@@ skipping 217 matching lines @@
         base::UserMetricsAction("MobileTabSwitcherCloseNonIncognitoTab"));
   }
 }
 
 - (void)tabSwitcherPanelControllerDidUpdateOverlayViewVisibility:
     (TabSwitcherPanelController*)tabSwitcherPanelController {
   [_tabSwitcherView updateOverlayButtonState];
 }
 
 @end