shared-highlight: Remove invalid DCHECK

This DCHECK is wrong since RequestSelector is a mojo method called from
the browser process. While requesting a selector should only happen from
a selection, this happens asynchronously so there's no guarantee the
frame will still have a selection by the time it receives this message.

Remove the DCHECK since we don't rely on selection in this method
anyway, it was used to start generation prior to receiving this message.

Bug: 1318211
Change-Id: I2ed9aaf92a7515e5d179d11fc2706b293b49f8c9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3767646
Reviewed-by: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Commit-Queue: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1026527}

third_party/blink/renderer/core/fragment_directive/text_fragment_handler.cc

@@ -52,7 +52,6 @@ void TextFragmentHandler::Cancel() {
 void TextFragmentHandler::RequestSelector(RequestSelectorCallback callback) {
   DCHECK(shared_highlighting::ShouldOfferLinkToText(
       GURL(GetFrame()->GetDocument()->Url())));
-  DCHECK(!GetFrame()->Selection().SelectedText().IsEmpty());
 
   response_callback_ = std::move(callback);
   selector_ready_status_ =