Change lookup path for Dart native extensions shared libraries.

runtime/bin/builtin.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("builtin");
 
 void print(arg) {
   _Logger._printString(arg.toString());
 }
 
@@ skipping 50 matching lines @@
 }
 
 String resolveUri(String base, String userString) {
   var baseUri = new Uri.fromString(base);
   _logResolution("# Resolving: $userString from $base");
   var resolved = baseUri.resolve(userString);
   _logResolution("# Resolved to: $resolved");
   return resolved.toString(); 
 }
 
+String resolveExtensionUri(String base, String userString) {
+  var uri = new Uri.fromString(userString);
+  if ("dart-ext" != uri.scheme) {
+    throw "Not a Dart extension uri: $uri";
+  }
+  var schemelessUri = new Uri(path: uri.path);
+  var baseUri = new Uri.fromString(base);
+  _logResolution("# Resolving: $userString from $base");
+  var resolved = baseUri.resolveUri(schemelessUri);
+  resolved = new Uri(scheme: 'dart-ext', path: resolved.path);
+  _logResolution("# Resolved to: $resolved");
+  return resolved.toString(); 
+}
+
 String filePathFromUri(String userUri) {
   var uri = new Uri.fromString(userUri);
   _logResolution("# Getting file path from: $uri");
   if ("file" != uri.scheme) {
     // Only handling file URIs in standalone binary.
     _logResolution("# Not a file URI.");
     throw "Not a file uri: $uri";
   }
   var path = uri.path;
   _logResolution("# Path: $path");
   if (_is_windows) {
     // Drop the leading / before the drive letter.
     path = path.substring(1);
     _logResolution("# path: $path");
   }
   return path;
 }