[iOS] Fix showing edit menu on long-press in location bar

The edit menu was being shown inside a DCHECK.
(I.e DCHECK([self methodWithSideEffects]). This meant that it was
stripped out in release builds, but not in debug, which is why this
didn't reproduce locally.

Bug: 1134647
Change-Id: Idbe1a48d0f9c82543cffcc3f79d05128e9589470
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2462266
Commit-Queue: Robbie Gibson <rkgibson@google.com>
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Auto-Submit: Robbie Gibson <rkgibson@google.com>
Reviewed-by: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815615}

ios/chrome/browser/ui/location_bar/location_bar_view_controller.mm

@@ -596,7 +596,7 @@ const NSString* kScribbleOmniboxElementId = @"omnibox";
         initWithTitle:l10n_util::GetNSString(IDS_IOS_SEARCH_COPIED_TEXT)
                action:@selector(searchCopiedText:)]);
 
-    DCHECK([self updateCachedClipboardStateWithCompletion:^() {
+    BOOL updateSuccessful = [self updateCachedClipboardStateWithCompletion:^() {
       if (@available(iOS 13, *)) {
         [menu showMenuFromView:self.view rect:self.locationBarSteadyView.frame];
       } else {
@@ -608,7 +608,8 @@ const NSString* kScribbleOmniboxElementId = @"omnibox";
       // presented menu.
       UIAccessibilityPostNotification(UIAccessibilityLayoutChangedNotification,
                                       menu);
-    }]);
+    }];
+    DCHECK(updateSuccessful);
   }
 }