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

components/data_reduction_proxy/core/common/data_reduction_proxy_event_store.cc

 // Copyright 2014 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 "components/data_reduction_proxy/core/common/data_reduction_proxy_event_store.h"
 
 #include <stddef.h>
 
 #include <utility>
 
 #include "base/json/json_writer.h"
 #include "base/memory/ptr_util.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/strings/string_piece.h"
 #include "base/strings/string_util.h"
 #include "base/time/time.h"
 #include "base/values.h"
 
 namespace {
 
 const size_t kMaxEventsToStore = 100;
 
 // Used by Data Reduction Proxy feedback reports. If the last bypass happened in
 // the last 5 minutes, the url will be cropped to only the host.
@@ skipping 19 matching lines @@
 // without having to keep an enum map in sync.
 const StringToConstant kDataReductionProxyBypassActionTypeTable[] = {
 #define BYPASS_ACTION_TYPE(label, value)                       \
   { #label, data_reduction_proxy::BYPASS_ACTION_TYPE_##label } \
   ,
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_bypass_action_list.h"
 #undef BYPASS_ACTION_TYPE
 };
 
 std::string JoinListValueStrings(base::ListValue* list_value) {
-  std::vector<std::string> values;
+  std::vector<base::StringPiece> values;
   for (const auto& value : *list_value) {
-    std::string value_string;
+    base::StringPiece value_string;
     if (!value->GetAsString(&value_string))
       return std::string();
 
-    values.push_back(std::move(value_string));
+    values.push_back(value_string);
   }
 
   return base::JoinString(values, ";");
 }
 
 }  // namespace
 
 namespace data_reduction_proxy {
 
 // static
@@ skipping 196 matching lines @@
       last_bypass->SetString("url", clean_url.spec());
     }
   }
 
   std::string json;
   base::JSONWriter::Write(*last_bypass.get(), &json);
   return json;
 }
 
 }  // namespace data_reduction_proxy