Minor refactor when adding to std::unordered_map

This patch uses the return value of |insert| to check if the
key is already in the map or not.

This patch has no behavior changes.

Bug: 652964
Change-Id: I6d53b923a7dbb8b39fdb03ec1a833ff8e88b5c9f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2462856
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816149}

content/browser/hyphenation/hyphenation_impl.cc

@@ -33,11 +33,11 @@ base::File GetDictionaryFile(const std::string& locale) {
   // Keep Files open in the cache for subsequent calls.
   static base::NoDestructor<DictionaryFileMap> cache;
 
-  const auto& it = cache->find(locale);
-  if (it != cache->end())
-    return it->second.Duplicate();
   const auto& inserted = cache->insert(std::make_pair(locale, base::File()));
   base::File& file = inserted.first->second;
+  // If the |locale| is already in the cache, duplicate the file and return it.
+  if (!inserted.second)
+    return file.Duplicate();
   DCHECK(!file.IsValid());
 
 #if defined(OS_ANDROID)