Vertical scrollbar flashes during auto grow

[Tade0]

Steps to reproduce

1. Go to: ​http://ckeditor.com/demo#auto-grow

Or create a CKEditor instance this way:

CKEDITOR.replace( 'editor', {
	extraPlugins: 'autogrow',
	autoGrow_maxHeight: 500
} );

2. Type enough lines for the editor to stop growing.

Expected result

The editor grows with its content.

Actual result

The editor grows, but with each step a vertical scrollbar appears for a fraction of a second.

[Tade0]

As a solution resizeEditor() could be called always twice - first time synchronously, and the second time after a timeout.

Changes pushed to ​branch:t/14698.