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

base/feature_list_unittest.cc

 // Copyright 2015 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 "base/feature_list.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <utility>
 
 #include "base/format_macros.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/persistent_memory_allocator.h"
+#include "base/strings/string_piece.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
 
 namespace {
 
 constexpr char kFeatureOnByDefaultName[] = "OnByDefault";
 struct Feature kFeatureOnByDefault {
   kFeatureOnByDefaultName, FEATURE_ENABLED_BY_DEFAULT
 };
 
 constexpr char kFeatureOffByDefaultName[] = "OffByDefault";
 struct Feature kFeatureOffByDefault {
   kFeatureOffByDefaultName, FEATURE_DISABLED_BY_DEFAULT
 };
 
 std::string SortFeatureListString(const std::string& feature_list) {
-  std::vector<std::string> features =
+  std::vector<base::StringPiece> features =
       FeatureList::SplitFeatureListString(feature_list);
   std::sort(features.begin(), features.end());
   return JoinString(features, ",");
 }
 
 }  // namespace
 
 class FeatureListTest : public testing::Test {
  public:
   FeatureListTest() : feature_list_(nullptr) {
@@ skipping 480 matching lines @@
   // Check that the field trials are still associated.
   FieldTrial* associated_trial1 =
       feature_list2->GetAssociatedFieldTrial(kFeatureOnByDefault);
   FieldTrial* associated_trial2 =
       feature_list2->GetAssociatedFieldTrial(kFeatureOffByDefault);
   EXPECT_EQ(associated_trial1, trial1);
   EXPECT_EQ(associated_trial2, trial2);
 }
 
 }  // namespace base