Don't unnecessarily copy strings

net/http/http_request_headers.cc

 // Copyright (c) 2012 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 "net/http/http_request_headers.h"
 
 #include "base/logging.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
@@ skipping 136 matching lines @@
     }
   } else if (value_index == header_line.size()) {
     SetHeader(header_key, "");
   } else {
     NOTREACHED();
   }
 }
 
 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", base::TRIM_WHITESPACE, base::SPLIT_WANT_NONEMPTY)) {
+    AddHeaderFromString(header);
   }
 }
 
 void HttpRequestHeaders::MergeFrom(const HttpRequestHeaders& other) {
   for (HeaderVector::const_iterator it = other.headers_.begin();
        it != other.headers_.end(); ++it ) {
     SetHeader(it->key, it->value);
   }
 }
 
@@ skipping 77 matching lines @@
   for (HeaderVector::const_iterator it = headers_.begin();
        it != headers_.end(); ++it) {
     if (base::EqualsCaseInsensitiveASCII(key, it->key))
       return it;
   }
 
   return headers_.end();
 }
 
 }  // namespace net