wp-calypso-15607-suggestions.patch

diff --git a/client/my-sites/preview/main.jsx b/client/my-sites/preview/main.jsx
index 119f0e53db..5327b2bef8 100644
--- a/client/my-sites/preview/main.jsx
+++ b/client/my-sites/preview/main.jsx
@@ -3,6 +3,7 @@
  */
 import { connect } from 'react-redux';
 import { localize } from 'i18n-calypso';
+import { throttle } from 'lodash';
 import React from 'react';
 import debugFactory from 'debug';
 
@@ -12,10 +13,11 @@ import debugFactory from 'debug';
 import {
 	getSelectedSite,
 	getSelectedSiteId,
+	hasSidebar,
 } from 'state/ui/selectors';
 import addQueryArgs from 'lib/route/add-query-args';
 import { setLayoutFocus } from 'state/ui/layout-focus/actions';
-import { isMobile } from 'lib/viewport';
+import { isWithinBreakpoint } from 'lib/viewport';
 
 import DocumentHead from 'components/data/document-head';
 import Main from 'components/main';
@@ -31,9 +33,25 @@ class PreviewMain extends React.Component {
 		previewUrl: null,
 	};
 
+	updateLayout = () => {
+		this.setState( {
+			showingClose: isWithinBreakpoint( '<660px' ),
+		} );
+	}
+
+	throttledUpdateLayout = throttle( this.updateLayout, 100 );
+
 	componentWillMount() {
+		this.updateLayout();
 		this.updateUrl();
-		this._isMobile = isMobile();
+	}
+
+	componentDidMount() {
+		global.window && global.window.addEventListener( 'resize', this.throttledUpdateLayout );
+	}
+
+	componentWillUnmount() {
+		global.window && global.window.removeEventListener( 'resize', this.throttledUpdateLayout );
 	}
 
 	updateUrl() {
@@ -79,7 +97,7 @@ class PreviewMain extends React.Component {
 			<Main className="preview">
 				<DocumentHead title={ translate( 'Site Preview' ) } />
 				<WebPreviewContent
-					showClose={ this._isMobile }
+					showClose={ this.state.showingClose }
 					onClose={ this.focusSidebar }
 					previewUrl={ this.state.previewUrl }
 				/>