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

lib/uri/uri.dart

Index: lib/uri/uri.dart
diff --git a/lib/uri/uri.dart b/lib/uri/uri.dart
index 7c6bfdd9ee27798c5c1495a5762bbf409dea254e..c05363827c9de9255f5c249067930e9082ae0446 100644
--- a/lib/uri/uri.dart
+++ b/lib/uri/uri.dart
@@ -171,6 +171,38 @@ class Uri {
     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, ':');