Fix few trivial Coverity issues, mainly PASS_BY_VALUE.

net/base/x509_certificate.h

 // Copyright (c) 2006-2008 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.
 
 #ifndef NET_BASE_X509_CERTIFICATE_H_
 #define NET_BASE_X509_CERTIFICATE_H_
 
 #include <string.h>
 
 #include <map>
@@ skipping 57 matching lines @@
 #elif defined(OS_LINUX)
   typedef struct CERTCertificateStr* OSCertHandle;
 #else
   // TODO(ericroman): not implemented
   typedef void* OSCertHandle;
 #endif
 
   // Principal represent an X.509 principal.
   struct Principal {
     Principal() { }
-    explicit Principal(std::string name) : common_name(name) { }
+    explicit Principal(const std::string& name) : common_name(name) { }
 
     // The different attributes for a principal.  They may be "".
     // Note that some of them can have several values.
 
     std::string common_name;
     std::string locality_name;
     std::string state_or_province_name;
     std::string country_name;
 
     std::vector<std::string> street_addresses;
@@ skipping 212 matching lines @@
 
   // Where the certificate comes from.
   Source source_;
 
   DISALLOW_COPY_AND_ASSIGN(X509Certificate);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_X509_CERTIFICATE_H_