Fix off-by-one in TokenizedString

Strings of size 1 don't have their single token picked up by
TokenizeWords, which is causing a crash in the LauncherSearchProvider.

Bug: 1140380
Change-Id: Ifb2815a1e9da79ffc0b51671d30ca87418e3170e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2515425
Commit-Queue: Tony Yeoman <tby@chromium.org>
Reviewed-by: Jia Meng <jiameng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823763}

chromeos/components/string_matching/tokenized_string.cc

@@ -98,7 +98,7 @@ void TokenizedString::TokenizeWords() {
   }
 
   // Generate the last token.
-  if (end - start > 1) {
+  if (end - start >= 1) {
     tokens_.emplace_back(base::i18n::ToLower(text_.substr(start, end - start)));
     mappings_.emplace_back(start, end);
   }

chromeos/components/string_matching/tokenized_string_unittest.cc

@@ -38,6 +38,13 @@ TEST(TokenizedStringTest, Empty) {
 }
 
 TEST(TokenizedStringTest, Basic) {
+  {
+    base::string16 text(base::UTF8ToUTF16("a"));
+    TokenizedString tokens(text);
+    EXPECT_EQ(base::UTF8ToUTF16("a{0,1}"), GetContent(tokens));
+    TokenizedString token_words(text, TokenizedString::Mode::kWords);
+    EXPECT_EQ(base::UTF8ToUTF16("a{0,1}"), GetContent(token_words));
+  }
   {
     base::string16 text(base::UTF8ToUTF16("ScratchPad"));
     TokenizedString tokens(text);