Reapply fast-URI patch.

runtime/lib/uri_patch.dart

Index: runtime/lib/uri_patch.dart
diff --git a/runtime/lib/uri_patch.dart b/runtime/lib/uri_patch.dart
index 2664b9b385930f312a94e9a7e737be58246a65fb..80024c2fb554aa2adec4310f292131415dea1142 100644
--- a/runtime/lib/uri_patch.dart
+++ b/runtime/lib/uri_patch.dart
@@ -16,14 +16,16 @@ Uri _unsupportedUriBase() {
 _UriBaseClosure _uriBaseClosure = _unsupportedUriBase;
 
 patch class Uri {
-  static final bool _isWindowsCached = _isWindowsPlatform;
-
-  /* patch */ static bool get _isWindows => _isWindowsCached;
-
   /* patch */ static Uri get base => _uriBaseClosure();
+}
+
+patch class _Uri {
+  static final bool _isWindowsCached = _isWindowsPlatform;
 
   static bool get _isWindowsPlatform native "Uri_isWindowsPlatform";
 
+  /* patch */ static bool get _isWindows => _isWindowsCached;
+
   /* patch */ static String _uriEncode(List<int> canonicalTable,
                                        String text,
                                        Encoding encoding,