[iOS] Change omnibox pre-edit exiting behavior.

This reverts the improvements introduced in
https://chromium-review.googlesource.com/c/chromium/src/+/1183495 on
iOS 13 due to a UIKit bug. This way, swiping on the system keyboard
does not hang the app and the keyboard. However, bugs 875918,873544
are regressing.

Bug: 988431, 875918, 873544
Change-Id: I91f358d80531d17104ffc6db96d4a488864325a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1722545Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Auto-Submit: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682196}

ios/chrome/browser/ui/omnibox/omnibox_view_ios.mm

@@ -438,13 +438,24 @@ bool OmniboxViewIOS::OnWillChange(NSRange range, NSString* new_text) {
     [field_ setClearingPreEditText:YES];
 
     // Exit the pre-editing state in OnWillChange() instead of OnDidChange(), as
-    // that allows IME to continue working.  The following code selects the text
-    // as if the pre-edit fake selection was real.
+    // that allows IME to continue working.
     [field_ exitPreEditState];
 
-    field_.selectedTextRange =
-        [field_ textRangeFromPosition:field_.beginningOfDocument
-                           toPosition:field_.endOfDocument];
+    if (@available(iOS 13, *)) {
+      // Exit pre-edit completely by setting the text to an empty string.
+      // On iOS 13, swiping keyboard acquires a lock that UITextField attempts
+      // to acquire when setSelectedTextRange: is called, causing a deadlock.
+      // Therefore this workaround is introduced. This probably introduces small
+      // issues with third-party keyboards, like crbug.com/875918 and
+      // crbug.com/873544. See crbug.com/988431 for more context.
+      [field_ setText:@""];
+    } else {
+      // The following code selects the text
+      // as if the pre-edit fake selection was real.
+      field_.selectedTextRange =
+          [field_ textRangeFromPosition:field_.beginningOfDocument
+                             toPosition:field_.endOfDocument];
+    }
 
     // Reset |range| to be of zero-length at location zero, as the field will be
     // now cleared.