[iOS] Make BVC able to become first responder

Allowing BVC to become first responder is letting it answer keyboard
shortcuts.
It also makes sure that the BVC is set as first responder when shown.

Fixed: 1088068
Change-Id: I04cab9d4d9e20487778f64b0cbba49d64f611408
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2235849Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#776923}

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

@@ -1337,6 +1337,10 @@ NSString* const kBrowserViewControllerSnackbarCategory =
 
 #pragma mark - UIResponder
 
+- (BOOL)canBecomeFirstResponder {
+  return YES;
+}
+
 - (NSArray*)keyCommands {
   if (![self shouldRegisterKeyboardCommands]) {
     return nil;

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

@@ -381,6 +381,8 @@
                                         toBrowser:self.bvcContainer
                                    withCompletion:^{
                                      extendedCompletion();
+                                     [self.bvcContainer
+                                             .currentBVC becomeFirstResponder];
                                    }];
 
   } else {