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

android_webview/browser/command_line_helper.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "android_webview/browser/command_line_helper.h"
 
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/feature_list.h"
 #include "base/stl_util.h"
+#include "base/strings/string_piece.h"
 #include "base/strings/string_util.h"
 #include "content/public/common/content_switches.h"
 
 using std::string;
 using std::vector;
 
 namespace {
 
 // Adds |feature_name| to the list of features in |feature_list_name|, but only
 // if the |feature_name| is absent from the list of features in both
 // |feature_list_name| and |other_feature_list_name|.
 void AddFeatureToList(base::CommandLine& command_line,
                       const string& feature_name,
                       const char* feature_list_name,
                       const char* other_feature_list_name) {
   const string features_list =
       command_line.GetSwitchValueASCII(feature_list_name);
   const string other_features_list =
       command_line.GetSwitchValueASCII(other_feature_list_name);
 
   if (features_list.empty() && other_features_list.empty()) {
     command_line.AppendSwitchASCII(feature_list_name, feature_name);
     return;
   }
 
-  vector<string> features =
+  vector<base::StringPiece> features =
       base::FeatureList::SplitFeatureListString(features_list);
-  vector<string> other_features =
+  vector<base::StringPiece> other_features =
       base::FeatureList::SplitFeatureListString(other_features_list);
 
   if (!base::ContainsValue(features, feature_name) &&
       !base::ContainsValue(other_features, feature_name)) {
     features.push_back(feature_name);
     command_line.AppendSwitchASCII(feature_list_name,
                                    base::JoinString(features, ","));
   }
 }
 
 }  // namespace
 
 // static
 void CommandLineHelper::AddEnabledFeature(base::CommandLine& command_line,
                                           const string& feature_name) {
   AddFeatureToList(command_line, feature_name, switches::kEnableFeatures,
                    switches::kDisableFeatures);
 }
 
 // static
 void CommandLineHelper::AddDisabledFeature(base::CommandLine& command_line,
                                            const string& feature_name) {
   AddFeatureToList(command_line, feature_name, switches::kDisableFeatures,
                    switches::kEnableFeatures);
 }