Added origin property to Uri class Added unit test coverage for origin property

lib/uri/uri.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #library('dart:uri');
 
 #import('dart:utf');
 
 #source('encode_decode.dart');
 #source('helpers.dart');
@@ skipping 153 matching lines @@
     }
     return new Uri.fromComponents(targetScheme, targetUserInfo, targetDomain,
                                   targetPort, targetPath, targetQuery,
                                   reference.fragment);
   }
 
   bool hasAuthority() {
     return (userInfo != "") || (domain != "") || (port != 0);
   }
 
+  /**
+   * For http/https schemes returns URI's [origin][] - scheme://domain:port.
+   * For all other schemes throws IllegalArgumentException.
+   * [origin]: http://www.w3.org/TR/2011/WD-html5-20110405/origin-0.html#origin
+   */
+  String get origin() {
+    if (scheme == "") {
+      // TODO(aprelev@gmail.com): Use StateException instead
+      throw new IllegalArgumentException("Cannot use origin without a scheme");
+    }
+    if (scheme != "http" && scheme != "https") {
+      // TODO(aprelev@gmail.com): Use StateException instead
+      throw new IllegalArgumentException(
+        "origin is applicable to http/https schemes only. Not \'$scheme\'");
+    }
+    StringBuffer sb = new StringBuffer();
+    sb.add(scheme);
+    sb.add(":");
+    if (domain == null || domain == "") {
+      // TODO(aprelev@gmail.com): Use StateException instead
+      throw new IllegalArgumentException("Cannot use origin without a domain");
+    }
+
+    sb.add("//");
+    sb.add(domain);
+    if (port != 0) {
+      sb.add(":");
+      sb.add(port);
+    }
+    return sb.toString();
+  }
+
   String toString() {
     StringBuffer sb = new StringBuffer();
     _addIfNonEmpty(sb, scheme, scheme, ':');
     if (hasAuthority() || (scheme == "file")) {
       sb.add("//");
       _addIfNonEmpty(sb, userInfo, userInfo, "@");
       sb.add(domain === null ? "null" : domain);
       if (port != 0) {
         sb.add(":");
         sb.add(port.toString());
       }
     }
     sb.add(path === null ? "null" : path);
     _addIfNonEmpty(sb, query, "?", query);
     _addIfNonEmpty(sb, fragment, "#", fragment);
     return sb.toString();
   }
 
   static void _addIfNonEmpty(StringBuffer sb, String test,
                              String first, String second) {
     if ("" != test) {
       sb.add(first === null ? "null" : first);
       sb.add(second === null ? "null" : second);
     }
   }
 }