TinyMCE wpView: scale iframes to 100% width and ensure they have transparent background. See #29048.

git-svn-id: https://develop.svn.wordpress.org/trunk@29545 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/js/tinymce/skins/wordpress/wp-content.css

@@ -366,6 +366,11 @@ audio {
 	}
 }
 
+.wpview-wrap .wpview-content > iframe {
+	max-width: 100%;
+	background: transparent;
+}
+
 #wp-image-toolbar {
 	position: absolute;
 	margin: 0;