Trivial: Language detection: prevent temporary string copies using const ref.

R=thestig,akihiroota

Change-Id: I7bf8774a761c41f602c887d1b4b4e92b9acd0f32
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2096406
Commit-Queue: Chris Hall <chrishall@chromium.org>
Reviewed-by: Akihiro Ota <akihiroota@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751283}

ui/accessibility/ax_language_detection.cc

@@ -118,8 +118,8 @@ void AXLanguageInfoStats::GenerateTopResults() {
 }
 
 void AXLanguageInfoStats::RecordLabelStatistics(
-    std::string labelled_lang,
-    std::string author_lang,
+    const std::string& labelled_lang,
+    const std::string& author_lang,
     bool labelled_with_first_result) {
   // Count the number of nodes we labelled, and the number we labelled with
   // our highest confidence result.
@@ -366,7 +366,7 @@ void AXLanguageDetectionManager::LabelLanguagesForNode(AXNode* node) {
     if (lang_info_stats_.CheckLanguageWithinTop(lang)) {
       lang_info->language = lang;
 
-      std::string author_lang = node->GetInheritedStringAttribute(
+      const std::string& author_lang = node->GetInheritedStringAttribute(
           ax::mojom::StringAttribute::kLanguage);
       lang_info_stats_.RecordLabelStatistics(lang, author_lang,
                                              labelled_with_first_result);

ui/accessibility/ax_language_detection.h

@@ -133,8 +133,8 @@ class AX_EXPORT AXLanguageInfoStats {
   // We consider the language we labelled the node with, the language the author
   // assigned, and whether or not we assigned our highest confidence detection
   // result.
-  void RecordLabelStatistics(std::string labelled_lang,
-                             std::string author_lang,
+  void RecordLabelStatistics(const std::string& labelled_lang,
+                             const std::string& author_lang,
                              bool labelled_with_first_result);
 
   // Update metrics to reflect we attempted to detect language for a node.