Cleanup: Pass std::string as const reference if possible

net/spdy/spdy_protocol.h

 // 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.
 
 // This file contains some protocol structures for use with SPDY 2 and 3
 // The SPDY 2 spec can be found at:
 // http://dev.chromium.org/spdy/spdy-protocol/spdy-protocol-draft2
 // The SPDY 3 spec can be found at:
 // http://dev.chromium.org/spdy/spdy-protocol/spdy-protocol-draft3
 
@@ skipping 951 matching lines @@
 class NET_EXPORT_PRIVATE SpdyAltSvcIR : public SpdyFrameWithStreamIdIR {
  public:
   explicit SpdyAltSvcIR(SpdyStreamId stream_id);
   ~SpdyAltSvcIR() override;
 
   std::string origin() const { return origin_; }
   const SpdyAltSvcWireFormat::AlternativeServiceVector& altsvc_vector() const {
     return altsvc_vector_;
   }
 
-  void set_origin(const std::string origin) { origin_ = origin; }
+  void set_origin(const std::string& origin) { origin_ = origin; }
   void add_altsvc(const SpdyAltSvcWireFormat::AlternativeService& altsvc) {
     altsvc_vector_.push_back(altsvc);
   }
 
   void Visit(SpdyFrameVisitor* visitor) const override;
 
  private:
   std::string origin_;
   SpdyAltSvcWireFormat::AlternativeServiceVector altsvc_vector_;
   DISALLOW_COPY_AND_ASSIGN(SpdyAltSvcIR);
@@ skipping 98 matching lines @@
   SpdyFrameVisitor() {}
   virtual ~SpdyFrameVisitor() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SpdyFrameVisitor);
 };
 
 }  // namespace net
 
 #endif  // NET_SPDY_SPDY_PROTOCOL_H_