Allow widget iframes to request camera and microphone permissions.

src/components/views/elements/AppTile.js

@@ -393,6 +393,10 @@ export default React.createClass({
         const sandboxFlags = "allow-forms allow-popups allow-popups-to-escape-sandbox "+
             "allow-same-origin allow-scripts allow-presentation";
 
+        // Additional iframe feature pemissions
+        // (see - https://sites.google.com/a/chromium.org/dev/Home/chromium-security/deprecating-permissions-in-cross-origin-iframes and https://wicg.github.io/feature-policy/)
+        const iframeFeatures = "microphone; camera; encrypted-media;";
+
         if (this.props.show) {
             const loadingElement = (
                 <div className='mx_AppTileBody mx_AppLoading'>
@@ -413,6 +417,8 @@ export default React.createClass({
                         <div className={this.state.loading ? 'mx_AppTileBody mx_AppLoading' : 'mx_AppTileBody'}>
                             { this.state.loading && loadingElement }
                             <iframe
+                                is
+                                allow={iframeFeatures}
                                 ref="appFrame"
                                 src={this._getSafeUrl()}
                                 allowFullScreen="true"