I cannot see how this block of code ever gets triggered.
  if (keyword_.empty()) {
    // Use the parser-generated new keyword from the URL in the OSDD for the
    // non-autodetected case.  The existing |keyword_| was generated from the
    // URL that hosted the OSDD, which results in the wrong keyword when the
    // OSDD was located on a third-party site that has nothing in common with
    // search engine described by OSDD.
    keyword_ = template_url_->keyword();
    DCHECK(!keyword_.empty());
  }
https://cs.chromium.org/chromium/src/components/search_engines/template_url_fetcher.cc?l=158-166

It appears to me that we always have a keyword.

This fragment is in the middle of TemplateURLFetcher::RequestDelegate::OnURLFetchComplete().  This function is only called when this class (a URL fetcher) has fetched a URL.

This class is only instantiated here:
https://cs.chromium.org/chromium/src/components/search_engines/template_url_fetcher.cc?l=249-250

Earlier in this function is
 DCHECK(!keyword.empty());
https://cs.chromium.org/chromium/src/components/search_engines/template_url_fetcher.cc?l=228

And this function is only called from one place also:
https://cs.chromium.org/chromium/src/chrome/browser/ui/search_engines/search_engine_tab_helper.cc?l=139-143

And a mere two lines above that call is
  if (keyword.empty())
    return;

Thus, I think the keyword can never be empty in template URL fetcher.  But I don't understand the comment there fully (it's likely got some history I'm not aware of), so I don't feel comfortable removing it.