Change lookup path for Dart native extensions shared libraries.

runtime/bin/builtin.dart

Index: runtime/bin/builtin.dart
diff --git a/runtime/bin/builtin.dart b/runtime/bin/builtin.dart
index b495346bf3aaae0925b368dbfcd23fe5bb82bdee..a963ed95f778c459ceee7200e10a006fd7c7cb7e 100644
--- a/runtime/bin/builtin.dart
+++ b/runtime/bin/builtin.dart
@@ -68,6 +68,20 @@ String resolveUri(String base, String userString) {
   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");