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

base/trace_event/trace_log.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/trace_event/trace_log.h"
 
 #include <algorithm>
 #include <cmath>
 #include <memory>
 #include <utility>
 
 #include "base/base_switches.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/leak_annotations.h"
 #include "base/location.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/ref_counted_memory.h"
 #include "base/memory/singleton.h"
 #include "base/message_loop/message_loop.h"
 #include "base/process/process_metrics.h"
 #include "base/stl_util.h"
+#include "base/strings/string_piece.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_tokenizer.h"
 #include "base/strings/stringprintf.h"
 #include "base/sys_info.h"
 #include "base/task_scheduler/post_task.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/thread_id_name_manager.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
 #include "base/trace_event/category_registry.h"
@@ skipping 1460 matching lines @@
                             "sort_index", process_sort_index_);
   }
 
   if (!process_name_.empty()) {
     InitializeMetadataEvent(AddEventToThreadSharedChunkWhileLocked(NULL, false),
                             current_thread_id, "process_name", "name",
                             process_name_);
   }
 
   if (!process_labels_.empty()) {
-    std::vector<std::string> labels;
+    std::vector<base::StringPiece> labels;
     for (const auto& it : process_labels_)
       labels.push_back(it.second);
     InitializeMetadataEvent(AddEventToThreadSharedChunkWhileLocked(NULL, false),
                             current_thread_id, "process_labels", "labels",
                             base::JoinString(labels, ","));
   }
 
   // Thread sort indices.
   for (const auto& it : thread_sort_indices_) {
     if (it.second == 0)
@@ skipping 206 matching lines @@
 }
 
 ScopedTraceBinaryEfficient::~ScopedTraceBinaryEfficient() {
   if (*category_group_enabled_) {
     TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(category_group_enabled_, name_,
                                                 event_handle_);
   }
 }
 
 }  // namespace trace_event_internal