Use of base::StringPairs appropriately in net/test/embedded_test_server/http_response.h

Bescause base/strings/string_split.h defines:
typedef std::vector<std::pair<std::string, std::string> > StringPairs;

BUG=412250

Review URL: https://codereview.chromium.org/1114843004

Cr-Commit-Position: refs/heads/master@{#327570}

net/test/embedded_test_server/http_response.h

@@ -7,10 +7,10 @@
 
 #include <map>
 #include <string>
-#include <vector>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
+#include "base/strings/string_split.h"
 #include "net/http/http_status_code.h"
 
 namespace net {
@@ -60,7 +60,7 @@ class BasicHttpResponse : public HttpResponse {
   HttpStatusCode code_;
   std::string content_;
   std::string content_type_;
-  std::vector<std::pair<std::string, std::string> > custom_headers_;
+  base::StringPairs custom_headers_;
 
   DISALLOW_COPY_AND_ASSIGN(BasicHttpResponse);
 };