Change uses of base::JoinString to pass StringPieces where possible.

chrome/browser/chrome_browser_main.cc

Index: chrome/browser/chrome_browser_main.cc
diff --git a/chrome/browser/chrome_browser_main.cc b/chrome/browser/chrome_browser_main.cc
index 8878bb270898338789a2d1de3c0f0acd08a4f04c..f2a8fad4e089511f7a2c7c5425c19c3f1a7fa99b 100644
--- a/chrome/browser/chrome_browser_main.cc
+++ b/chrome/browser/chrome_browser_main.cc
@@ -31,6 +31,7 @@
 #include "base/run_loop.h"
 #include "base/strings/string16.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/strings/string_piece.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/sys_info.h"
@@ -853,8 +854,8 @@ void ChromeBrowserMainParts::SetupOriginTrialsCommandLine() {
     const base::ListValue* override_disabled_feature_list =
         local_state_->GetList(prefs::kOriginTrialDisabledFeatures);
     if (override_disabled_feature_list) {
-      std::vector<std::string> disabled_features;
-      std::string disabled_feature;
+      std::vector<base::StringPiece> disabled_features;
+      base::StringPiece disabled_feature;
       for (const auto& item : *override_disabled_feature_list) {
         if (item->GetAsString(&disabled_feature)) {
           disabled_features.push_back(disabled_feature);