Revert of Move JoinString to the base namespace

chromecast/base/metrics/cast_metrics_helper.cc

Index: chromecast/base/metrics/cast_metrics_helper.cc
diff --git a/chromecast/base/metrics/cast_metrics_helper.cc b/chromecast/base/metrics/cast_metrics_helper.cc
index 218da4ac8b79f8e4109b4dd5e613641a6d48f205..6d07b4a93413c14cb1d2c4434a1ccf714f0193f3 100644
--- a/chromecast/base/metrics/cast_metrics_helper.cc
+++ b/chromecast/base/metrics/cast_metrics_helper.cc
@@ -78,14 +78,12 @@
     const std::string& app_id,
     const std::string& session_id,
     const std::string& sdk_version) {
-  std::string result(action_name);
-  result.push_back(kMetricsNameAppInfoDelimiter);
-  result.append(app_id);
-  result.push_back(kMetricsNameAppInfoDelimiter);
-  result.append(session_id);
-  result.push_back(kMetricsNameAppInfoDelimiter);
-  result.append(sdk_version);
-  return result;
+  std::vector<std::string> parts;
+  parts.push_back(action_name);
+  parts.push_back(app_id);
+  parts.push_back(session_id);
+  parts.push_back(sdk_version);
+  return JoinString(parts, kMetricsNameAppInfoDelimiter);
 }
 
 // static