Create 'unified' version of Date, with a dart2js implementation.

lib/compiler/implementation/compiler.dart

 // Copyright (c) 2012, 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.
 
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
 final bool REPORT_EXCESS_RESOLUTION = false;
@@ skipping 538 matching lines @@
     delayedPatches.forEach((String path, LibraryElement importedLibrary) {
       patchDartLibrary(importedLibrary, path);
     });
   }
 
   void applyContainerPatch(ContainerElement original, Link<Element> patches,
                            Element lookup(SourceString name)) {
     while (!patches.isEmpty()) {
       Element patchElement = patches.head;
       Element originalElement = lookup(patchElement.name);
-      // Getters and setters are kept inside a synthetic field.
-      if (patchElement.kind === ElementKind.ABSTRACT_FIELD) {
+      if (patchElement.isAccessor()) {
+        // Skip accessors. An accessor always has an abstract field,
+        // representing the accessor in the lookup scope. We can thus skip the
+        // accessors and just handle the abstract field.
+      } else if (patchElement.kind === ElementKind.ABSTRACT_FIELD) {
+        // Getters and setters are kept inside a synthetic field.
         if (originalElement !== null &&
             originalElement.kind !== ElementKind.ABSTRACT_FIELD) {
           internalError("Cannot patch non-getter/setter with getter/setter",
                         element: originalElement);
         }
         AbstractFieldElement patchField = patchElement;
         AbstractFieldElement originalField = originalElement;
         if (patchField.getter !== null) {
           if (originalField === null || originalField.getter === null) {
             original.addGetterOrSetter(clonePatch(patchField.getter),
@@ skipping 520 matching lines @@
     final endOffset = end.charOffset + end.slowCharCount;
 
     // [begin] and [end] might be the same for the same empty token. This
     // happens for instance when scanning '$$'.
     assert(endOffset >= beginOffset);
     return f(beginOffset, endOffset);
   }
 
   String toString() => 'SourceSpan($uri, $begin, $end)';
 }