Split _uriEncode into JS and VM versions.

sdk/lib/_internal/js_runtime/lib/core_patch.dart

Index: sdk/lib/_internal/js_runtime/lib/core_patch.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/core_patch.dart b/sdk/lib/_internal/js_runtime/lib/core_patch.dart
index 7d6ad7c244533fc8af009361b01a016c19aae16b..a9832709b21b2fe46243d8e73e18eb8874e2c62c 100644
--- a/sdk/lib/_internal/js_runtime/lib/core_patch.dart
+++ b/sdk/lib/_internal/js_runtime/lib/core_patch.dart
@@ -527,6 +527,47 @@ class Uri {
     if (uri != null) return Uri.parse(uri);
     throw new UnsupportedError("'Uri.base' is not supported");
   }
+
+
+  // Matches a String that _uriEncodes to itself regardless of the kind of
+  // component.  This corresponds to [_unreservedTable], i.e. characters that
+  // are not encoded by any encoding table.
+  static final RegExp _needsNoEncoding = new RegExp(r'^[\-\.0-9A-Z_a-z~]*$');
+
+  /**
+   * This is the internal implementation of JavaScript's encodeURI function.
+   * It encodes all characters in the string [text] except for those
+   * that appear in [canonicalTable], and returns the escaped string.
+   */
+  @patch
+  static String _uriEncode(List<int> canonicalTable,
+                           String text,
+                           Encoding encoding,
+                           bool spaceToPlus) {
+    if (identical(encoding, UTF8) && _needsNoEncoding.hasMatch(text)) {
+      return text;
+    }
+
+    // Encode the string into bytes then generate an ASCII only string
+    // by percent encoding selected bytes.
+    StringBuffer result = new StringBuffer();
+    var bytes = encoding.encode(text);
+    for (int i = 0; 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);
+        result.writeCharCode(hexDigits.codeUnitAt(byte >> 4));
+        result.writeCharCode(hexDigits.codeUnitAt(byte & 0x0f));
+      }
+    }
+    return result.toString();
+  }
 }
 
 @patch