Fix bugs in Uri: Allow empty port, handle path starting with "//" in toString.

sdk/lib/core/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.
 
 part of dart.core;
 
 /**
  * A parsed URI, such as a URL.
  *
  * **See also:**
@@ skipping 216 matching lines @@
         index++;
         char = EOI;
       }
       int hostStart = authStart;
       int hostEnd = index;
       if (lastAt >= 0) {
         userinfo = _makeUserInfo(uri, authStart, lastAt);
         hostStart = lastAt + 1;
       }
       if (lastColon >= 0) {
-        if (lastColon + 1 == index) {
-          _fail(uri, index, "Invalid port number");
-        }
         int portNumber = 0;
         for (int i = lastColon + 1; i < index; i++) {
           int digit = uri.codeUnitAt(i);
           if (_ZERO > digit || _NINE < digit) {
             _fail(uri, i, "Invalid port number");
           }
           portNumber = portNumber * 10 + (digit - _ZERO);
         }
         port = _makePort(portNumber, scheme);
         hostEnd = lastColon;
@@ skipping 1228 matching lines @@
     ss.write(_host == null ? "null" : _host);
     if (_port != 0) {
       ss.write(":");
       ss.write(_port.toString());
     }
   }
 
   String toString() {
     StringBuffer sb = new StringBuffer();
     _addIfNonEmpty(sb, scheme, scheme, ':');
-    if (hasAuthority || (scheme == "file")) {
+    if (hasAuthority || path.startsWith("//") || (scheme == "file")) {
+      // File URIS always have the authority, even if it is empty.
+      // The empty URI means "localhost".
       sb.write("//");
       _writeAuthority(sb);
     }
     sb.write(path);
     _addIfNonEmpty(sb, query, "?", query);
     _addIfNonEmpty(sb, fragment, "#", fragment);
     return sb.toString();
   }
 
   bool operator==(other) {
@@ skipping 697 matching lines @@
       0xafff,   // 0x30 - 0x3f  1111111111110101
                 //              @ABCDEFGHIJKLMNO
       0xffff,   // 0x40 - 0x4f  1111111111111111
                 //              PQRSTUVWXYZ    _
       0x87ff,   // 0x50 - 0x5f  1111111111100001
                 //               abcdefghijklmno
       0xfffe,   // 0x60 - 0x6f  0111111111111111
                 //              pqrstuvwxyz   ~
       0x47ff];  // 0x70 - 0x7f  1111111111100010
 }