[iOS] Set BVC as first responder only if there isn't one

This CL makes sure to check that there isn't a first responder before
setting BVC as first responder.
The omnibox can be the first resonder at that point when opened from
3D touch.

Fixed: 1103635
Change-Id: I901bebd33ceced169d9848ca8c785d5ef8913ca1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2315035
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Auto-Submit: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792180}

ios/chrome/browser/ui/tab_grid/BUILD.gn

@@ -41,6 +41,7 @@ source_set("tab_grid") {
     "//ios/chrome/browser/ui/recent_tabs",
     "//ios/chrome/browser/ui/recent_tabs:recent_tabs_ui",
     "//ios/chrome/browser/ui/tab_grid/transitions",
+    "//ios/chrome/browser/ui/util",
     "//ios/chrome/browser/url_loading",
     "//ios/chrome/browser/web",
     "//ios/chrome/browser/web_state_list",

ios/chrome/browser/ui/tab_grid/tab_grid_coordinator.mm

@@ -28,6 +28,7 @@
 #import "ios/chrome/browser/ui/tab_grid/tab_grid_view_controller.h"
 #import "ios/chrome/browser/ui/tab_grid/transitions/tab_grid_transition_handler.h"
 #include "ios/chrome/browser/ui/ui_feature_flags.h"
+#import "ios/chrome/browser/ui/util/uikit_ui_util.h"
 #import "ios/chrome/browser/url_loading/url_loading_params.h"
 #import "ios/chrome/browser/web_state_list/web_state_list.h"
 
@@ -363,7 +364,11 @@
     [self.tabSwitcher.delegate
         tabSwitcherDismissTransitionDidEnd:self.tabSwitcher];
     if (base::FeatureList::IsEnabled(kContainedBVC)) {
-      [self.bvcContainer.currentBVC becomeFirstResponder];
+      if (!GetFirstResponder()) {
+        // It is possible to already have a first responder (for example the
+        // omnibox). In that case, we don't want to mark BVC as first responder.
+        [self.bvcContainer.currentBVC becomeFirstResponder];
+      }
     }
     if (completion) {
       completion();