Split _uriEncode into JS and VM versions.

runtime/lib/uri_patch.dart

 // Copyright (c) 2013, 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.
 
+import "dart:convert" show ASCII;
+
 // VM implementation of Uri.
 typedef Uri _UriBaseClosure();
 
 Uri _unsupportedUriBase() {
   throw new UnsupportedError("'Uri.base' is not supported");
 }
 
 // _uriBaseClosure can be overwritten by the embedder to supply a different
 // value for Uri.base.
 _UriBaseClosure _uriBaseClosure = _unsupportedUriBase;
 
 patch class Uri {
   static final bool _isWindowsCached = _isWindowsPlatform;
 
   /* patch */ static bool get _isWindows => _isWindowsCached;
 
   /* patch */ static Uri get base => _uriBaseClosure();
 
   static bool get _isWindowsPlatform native "Uri_isWindowsPlatform";
+
+  /* patch */ static String _uriEncode(List<int> canonicalTable,
+                                       String text,
+                                       Encoding encoding,
+                                       bool spaceToPlus) {
+    // First check if the text will be changed by encoding.
+    int i = 0;
+    if (identical(encoding, UTF8) ||
+        identical(encoding, LATIN1) ||
+        identical(encoding, ASCII)) {
+      // Encoding is compatible with the original string.
+      // Find first character that needs encoding.
+      for (; i < text.length; i++) {
+        var char = text.codeUnitAt(i);
+        if (char >= 128 ||
+            canonicalTable[char >> 4] & (1 << (char & 0x0f)) == 0) {
+          break;
+        }
+      }
+    }
+    if (i == text.length) return text;
+
+    // Encode the string into bytes then generate an ASCII only string
+    // by percent encoding selected bytes.
+    StringBuffer result = new StringBuffer();
+    for (int j = 0; j < i; j++) {
+      result.writeCharCode(text.codeUnitAt(j));
+    }
+
+    // TODO(lrn): Is there a way to only encode from index i and forwards.
+    var bytes = encoding.encode(text);
+    for (; i < bytes.length; i++) {
+      int byte = bytes[i];
+      if (byte < 128 &&
+          ((canonicalTable[byte >> 4] & (1 << (byte & 0x0f))) != 0)) {
+        result.writeCharCode(byte);
+      } else if (spaceToPlus && byte == _SPACE) {
+        result.writeCharCode(_PLUS);
+      } else {
+        const String hexDigits = '0123456789ABCDEF';
+        result..writeCharCode(_PERCENT)
+              ..writeCharCode(hexDigits.codeUnitAt(byte >> 4))
+              ..writeCharCode(hexDigits.codeUnitAt(byte & 0x0f));
+      }
+    }
+    return result.toString();
+  }
 }