Don't unnecessarily copy strings

net/http/http_request_headers.cc

Index: net/http/http_request_headers.cc
diff --git a/net/http/http_request_headers.cc b/net/http/http_request_headers.cc
index c2eee59af95f8408a9d11ad774986e302270175b..ce646dc20817144e0fb51aa971994c8a88f8f86d 100644
--- a/net/http/http_request_headers.cc
+++ b/net/http/http_request_headers.cc
@@ -154,15 +154,10 @@ void HttpRequestHeaders::AddHeaderFromString(
 
 void HttpRequestHeaders::AddHeadersFromString(
     const base::StringPiece& headers) {
-  // TODO(willchan): Consider adding more StringPiece support in string_util.h
-  // to eliminate copies.
-  std::vector<std::string> header_line_vector;
-  base::SplitStringUsingSubstr(headers.as_string(), "\r\n",
-                               &header_line_vector);
-  for (std::vector<std::string>::const_iterator it = header_line_vector.begin();
-       it != header_line_vector.end(); ++it) {
-    if (!it->empty())
-      AddHeaderFromString(*it);
+  for (const base::StringPiece& header :
+       base::SplitStringPieceUsingSubstr(headers, "\r\n")) {
+    if (!header.empty())
+      AddHeaderFromString(header);
   }
 }