Remove a few un-necessary string copies in net/

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 841d4df133fdaa78c94b7d0341e1ccadd7d114e8..298c5e4daaf9bb9e7d23fd61f0d1f5901aebdf5e 100644
--- a/net/http/http_request_headers.cc
+++ b/net/http/http_request_headers.cc
@@ -85,16 +85,16 @@ void HttpRequestHeaders::SetHeader(const base::StringPiece& key,
                                    const base::StringPiece& value) {
   HeaderVector::iterator it = FindHeader(key);
   if (it != headers_.end())
-    it->value = value.as_string();
+    it->value.assign(value.data(), value.size());
   else
-    headers_.push_back(HeaderKeyValuePair(key.as_string(), value.as_string()));
+    headers_.push_back(HeaderKeyValuePair(key, value));
 }
 
 void HttpRequestHeaders::SetHeaderIfMissing(const base::StringPiece& key,
                                             const base::StringPiece& value) {
   HeaderVector::iterator it = FindHeader(key);
   if (it == headers_.end())
-    headers_.push_back(HeaderKeyValuePair(key.as_string(), value.as_string()));
+    headers_.push_back(HeaderKeyValuePair(key, value));
 }
 
 void HttpRequestHeaders::RemoveHeader(const base::StringPiece& key) {