Use base::StringTokenizer::token_piece() when std::string is not needed.

base::StringTokenizer::token() creates a new std::string each time. Many
callers do not even need a std::string, so just update them to use
token_piece() instead.

This CL was uploaded by git cl split.

R=ellyjones@chromium.org

Bug: 1199547
Change-Id: I6d17089d3e68268914f4cff963be7055989863e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2832869
Auto-Submit: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#873965}

components/flags_ui/flags_state.cc

@@ -190,10 +190,8 @@ std::set<std::string> TokenizeOriginList(const std::string& value) {
   base::StringTokenizer tokenizer(input, delimiters);
   std::set<std::string> origin_strings;
   while (tokenizer.GetNext()) {
-    const std::string token = tokenizer.token();
-    if (token.empty()) {
-      continue;
-    }
+    base::StringPiece token = tokenizer.token_piece();
+    DCHECK(!token.empty());
     const GURL url(token);
     if (!url.is_valid() ||
         (!url.SchemeIsHTTPOrHTTPS() && !url.SchemeIsWSOrWSS())) {