Rewrite std::string("") to std::string(), Linux edition.

net/http/http_auth.cc

Index: net/http/http_auth.cc
diff --git a/net/http/http_auth.cc b/net/http/http_auth.cc
index fb7fc5dc2cf1dd8901413644a774f8ef668c5580..9e9410b6e8bf287a66ebeab4022847efd1537f27 100644
--- a/net/http/http_auth.cc
+++ b/net/http/http_auth.cc
@@ -146,7 +146,7 @@ std::string HttpAuth::GetChallengeHeaderName(Target target) {
       return "WWW-Authenticate";
     default:
       NOTREACHED();
-      return "";
+      return std::string();
   }
 }
 
@@ -159,7 +159,7 @@ std::string HttpAuth::GetAuthorizationHeaderName(Target target) {
       return HttpRequestHeaders::kAuthorization;
     default:
       NOTREACHED();
-      return "";
+      return std::string();
   }
 }
 
@@ -172,7 +172,7 @@ std::string HttpAuth::GetAuthTargetString(Target target) {
       return "server";
     default:
       NOTREACHED();
-      return "";
+      return std::string();
   }
 }