[iOS][Getaway] Cancel omnibox edit when showing the blocking UI.

If the omnibox is editing when an incognito goes background, the blocker
should not allow for keyboard input.

Bug: 1160681
Change-Id: I55f4fa10a4ea97af01e4a96afe9d999d4a0d4cbb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2600906
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Auto-Submit: Stepan Khapugin <stkhapugin@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#839126}

ios/chrome/browser/ui/browser_view/browser_view_controller.mm

@@ -4817,6 +4817,13 @@ NSString* const kBrowserViewControllerSnackbarCategory =
     [self.view addSubview:self.blockingView];
     AddSameConstraints(self.view, self.blockingView);
     self.blockingView.alpha = 1;
+    [self.omniboxHandler cancelOmniboxEdit];
+
+    // Resign the first responder. This achieves multiple goals:
+    // 1. The keyboard is dismissed.
+    // 2. Hardware keyboard events (such as space to scroll) will be ignored.
+    UIResponder* firstResponder = GetFirstResponder();
+    [firstResponder resignFirstResponder];
   } else {
     [UIView animateWithDuration:0.2
         animations:^{