Follow up from ARC conversion

ios/chrome/browser/ui/toolbar/web_toolbar_controller.mm

Index: ios/chrome/browser/ui/toolbar/web_toolbar_controller.mm
diff --git a/ios/chrome/browser/ui/toolbar/web_toolbar_controller.mm b/ios/chrome/browser/ui/toolbar/web_toolbar_controller.mm
index 528b23ab18dc32ffb78447b53a0c391428192bc7..b306ba342f959c525ad96cc90242c99223c9c634 100644
--- a/ios/chrome/browser/ui/toolbar/web_toolbar_controller.mm
+++ b/ios/chrome/browser/ui/toolbar/web_toolbar_controller.mm
@@ -849,7 +849,7 @@ CGRect RectShiftedDownAndResizedForStatusBar(CGRect rect) {
 - (void)dismissTabHistoryPopup {
   if (!_tabHistoryPopupController)
     return;
-  TabHistoryPopupController* tempTHPC = _tabHistoryPopupController;
+  __block TabHistoryPopupController* tempTHPC = _tabHistoryPopupController;
   [tempTHPC containerView].userInteractionEnabled = NO;
   [tempTHPC dismissAnimatedWithCompletion:^{
     // Unpress the back/forward button by restoring the normal and
@@ -857,7 +857,7 @@ CGRect RectShiftedDownAndResizedForStatusBar(CGRect rect) {
     [self setImagesForNavButton:_backButton withTabHistoryVisible:NO];
     [self setImagesForNavButton:_forwardButton withTabHistoryVisible:NO];
     // Reference tempTHPC so the block retains it.
-    [tempTHPC self];
+    tempTHPC = nil;
   }];
   // reset _tabHistoryPopupController to prevent -applicationDidEnterBackground
   // from posting another kTabHistoryPopupWillHideNotification.