Fix typo in documentation of CanvasElement.toDataUrl.

sdk/lib/html/dart2js/html_dart2js.dart

 /// The Dart HTML library.
 library dart.dom.html;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:_collection-dev' hide Symbol;
 import 'dart:html_common';
 import 'dart:indexed_db';
 import 'dart:isolate';
 import 'dart:json' as json;
@@ skipping 837 matching lines @@
    *
    * If the type requested is not 'image/png', and the returned value is
    * 'data:image/png', then the requested type is not supported.
    *
    * Example usage:
    *
    *     CanvasElement canvas = new CanvasElement();
    *     var ctx = canvas.context2D
    *     ..fillStyle = "rgb(200,0,0)"
    *     ..fillRect(10, 10, 55, 50);
-   *     var dataUrl = canvas.toDataURL("image/jpeg", 0.95);
+   *     var dataUrl = canvas.toDataUrl("image/jpeg", 0.95);
    *     // The Data Uri would look similar to
    *     // 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUA
    *     // AAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO
    *     // 9TXL0Y4OHwAAAABJRU5ErkJggg=='
    *     //Create a new image element from the data URI.
    *     var img = new ImageElement();
    *     img.src = dataUrl;
    *     document.body.children.add(img);
    *
    * See also:
@@ skipping 28736 matching lines @@
       _position = nextPosition;
       return true;
     }
     _current = null;
     _position = _array.length;
     return false;
   }
 
   T get current => _current;
 }