Cleanup: Pass std::string as const reference from chrome/

chrome/renderer/searchbox/searchbox_extension.cc

Index: chrome/renderer/searchbox/searchbox_extension.cc
diff --git a/chrome/renderer/searchbox/searchbox_extension.cc b/chrome/renderer/searchbox/searchbox_extension.cc
index 0113c712d1d45f194874078d51d3f5d5dece3b8a..5ff90824b7f1d4cafc606f35151b53875dd2a401 100644
--- a/chrome/renderer/searchbox/searchbox_extension.cc
+++ b/chrome/renderer/searchbox/searchbox_extension.cc
@@ -117,7 +117,8 @@ v8::Local<v8::String> GenerateThumbnailURL(
           "chrome-search://thumb/%d/%d", render_view_id, most_visited_item_id));
 }
 
-v8::Local<v8::String> GenerateThumb2URL(v8::Isolate* isolate, std::string url) {
+v8::Local<v8::String> GenerateThumb2URL(v8::Isolate* isolate,
+                                        const std::string& url) {
   return UTF8ToV8String(
       isolate, base::StringPrintf("chrome-search://thumb2/%s", url.c_str()));
 }