fix spelling in core libraries

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 205 matching lines @@
       // TODO(sra).
       throw new UnimplementedError('structured clone of RegExp');
     }
 
     if (isJavaScriptPromise(e)) {
       return convertNativePromiseToDartFuture(e);
     }
 
     if (isJavaScriptSimpleObject(e)) {
       // TODO(sra): If mustCopy is false, swizzle the prototype for one of a Map
-      // implementation that uses the properies as storage.
+      // implementation that uses the properties as storage.
       var slot = findSlot(e);
       var copy = readSlot(slot);
       if (copy != null) return copy;
       copy = {};
 
       writeSlot(slot, copy);
       forEachJsField(e, (key, value) => copy[key] = walk(value));
       return copy;
     }
 
@@ skipping 107 matching lines @@
 
 // We can get rid of this conversion if _TypedImageData implements the fields
 // with native names.
 convertDartToNative_ImageData(ImageData imageData) {
   if (imageData is _TypedImageData) {
     return JS('', '{data: #, height: #, width: #}',
         imageData.data, imageData.height, imageData.width);
   }
   return imageData;
 }