Emit compile-time error for incorrectly used optional parameters.

sdk/lib/html/html_common/conversions.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.
 
 
 // Conversions for IDBKey.
 //
 // Per http://www.w3.org/TR/IndexedDB/#key-construct
 //
 // "A value is said to be a valid key if it is one of the following types: Array
@@ skipping 201 matching lines @@
  * [object] is the result of a structured clone operation.
  *
  * If necessary, JavaScript Dates are converted into Dart Dates.
  *
  * If [mustCopy] is [:true:], the entire object is copied and the original input
  * is not mutated.  This should be the case where Dart and JavaScript code can
  * access the value, for example, via multiple event listeners for
  * MessageEvents.  Mutating the object to make it more 'Dart-like' would corrupt
  * the value as seen from the JavaScript listeners.
  */
-convertNativeToDart_AcceptStructuredClone(object, {mustCopy = false}) {
+convertNativeToDart_AcceptStructuredClone(object, {mustCopy: false}) {
 
   // TODO(sra): Replace slots with identity hash table that works on non-dart
   // objects.
   var values = [];
   var copies = [];
 
   int findSlot(value) {
     int length = values.length;
     for (int i = 0; i < length; i++) {
       if (identical(values[i], value)) return i;
@@ skipping 118 matching lines @@
 const String _serializedScriptValue =
     'num|String|bool|'
     'JSExtendableArray|=Object|'
     'Blob|File|ByteBuffer|TypedData'
     // TODO(sra): Add Date, RegExp.
     ;
 const annotation_Creates_SerializedScriptValue =
     const Creates(_serializedScriptValue);
 const annotation_Returns_SerializedScriptValue =
     const Returns(_serializedScriptValue);