Use JavaScript to detect if Selection.modify is available.

dart/site/try/src/interaction_manager.dart

 // Copyright (c) 2014, 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 trydart.interaction_manager;
 
 import 'dart:html';
 
 import 'dart:convert' show
     JSON;
 
 import 'dart:math' show
     max,
     min;
 
 import 'dart:async' show
     Completer,
     Future,
     Timer;
 
 import 'dart:collection' show
     Queue;
 
-import 'dart:js' as hack;
-
 import 'package:compiler/implementation/scanner/scannerlib.dart' show
     BeginGroupToken,
     EOF_TOKEN,
     ErrorToken,
     STRING_INTERPOLATION_IDENTIFIER_TOKEN,
     STRING_INTERPOLATION_TOKEN,
     STRING_TOKEN,
     StringScanner,
     Token,
     UnmatchedToken,
@@ skipping 1260 matching lines @@
       message == "Inferring types..." ||
       message == "Compiling..." ||
       message.startsWith('Compiled ');
 }
 
 void workAroundFirefoxBug() {
   Selection selection = window.getSelection();
   if (!isCollapsed(selection)) return;
   Node node = selection.anchorNode;
   int offset = selection.anchorOffset;
-  if (selection.anchorNode is Element && selection.anchorOffset != 0) {
+  if (node is Element && offset != 0) {
     // In some cases, Firefox reports the wrong anchorOffset (always seems to
     // be 6) when anchorNode is an Element. Moving the cursor back and forth
     // adjusts the anchorOffset.
     // Safari can also reach this code, but the offset isn't wrong, just
     // inconsistent.  After moving the cursor back and forth, Safari will make
     // the offset relative to a text node.
-    // TODO(ahe): Come up with a better way to encapsulate the method below.
-    var selectionProxy = new hack.JsObject.fromBrowserObject(selection);
-    var modify = selectionProxy['modify'];
-    if (modify != null) {
+    if (settings.hasSelectionModify.value) {
       // IE doesn't support selection.modify, but it's okay since the code
       // above is for Firefox, IE doesn't have problems with anchorOffset.
       selection
           ..modify('move', 'backward', 'character')
           ..modify('move', 'forward', 'character');
       print('Selection adjusted $node@$offset -> '
             '${selection.anchorNode}@${selection.anchorOffset}.');
     }
   }
 }
@@ skipping 20 matching lines @@
     token = token.next;
     kind = token.kind;
   }
   return token;
 }
 
 String extractQuote(String string) {
   StringQuoting q = StringValidator.quotingFromString(string);
   return (q.raw ? 'r' : '') + (q.quoteChar * q.leftQuoteLength);
 }