Constify SchemeHostPort and Origin accessors.

BUG=490074
R=rsleevi@chromium.org,brettw@chromium.org

Review URL: https://codereview.chromium.org/1229003007

Cr-Commit-Position: refs/heads/master@{#339846}

url/origin.h

@@ -89,11 +89,8 @@ class URL_EXPORT Origin {
   ~Origin();
 
   // For unique origins, these return ("", "", 0).
-  //
-  // TODO(mkwst): These should be 'const std::string&', along with their
-  // 'url::SchemeHostPort' analogs.
-  std::string scheme() const { return tuple_.scheme(); }
-  std::string host() const { return tuple_.host(); }
+  const std::string& scheme() const { return tuple_.scheme(); }
+  const std::string& host() const { return tuple_.host(); }
   uint16 port() const { return tuple_.port(); }
 
   bool unique() const { return unique_; }

url/scheme_host_port.h

@@ -96,8 +96,8 @@ class URL_EXPORT SchemeHostPort {
   // Returns the host component, in URL form. That is all IDN domain names will
   // be expressed as A-Labels ('☃.net' will be returned as 'xn--n3h.net'), and
   // and all IPv6 addresses will be enclosed in brackets ("[2001:db8::1]").
-  std::string host() const { return host_; }
-  std::string scheme() const { return scheme_; }
+  const std::string& host() const { return host_; }
+  const std::string& scheme() const { return scheme_; }
   uint16 port() const { return port_; }
   bool IsInvalid() const;