Site Icon: Show correct background preview for transparent images.

iOS will show transparent parts as black, where as the icon itself stays
transparent when used as a favicon.

See #16434.


git-svn-id: https://develop.svn.wordpress.org/trunk@33049 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/css/site-icon.css

@@ -49,6 +49,7 @@
 }
 
 .site-icon-crop-preview-homeicon {
+	background-color: #000;
 	-webkit-border-radius: 16px;
 	border-radius: 16px;
 	height: 64px;

src/wp-admin/js/site-icon-crop.js

@@ -39,6 +39,7 @@
 		ready: function() {
 			jcrop_api = $.Jcrop( '#crop-image' );
 			jcrop_api.setOptions({
+				bgColor: 'transparent',
 				aspectRatio: 1,
 				onSelect: siteIconCrop.updateCoords,
 				onChange: siteIconCrop.updateCoords,