Updated CSS for DraftEditorPlaceholder to support multiline placeholder

Summary: Updated CSS to show a line break in case the placeholder text contains a newline.

Reviewed By: sophiebits

Differential Revision: D6361301

fbshipit-source-id: 8db9baeac60321835b23cda392555e1bf03bdfd0

src/component/base/DraftEditorPlaceholder.react.js

@@ -50,11 +50,16 @@ class DraftEditorPlaceholder extends React.Component<Props> {
       'public/DraftEditorPlaceholder/hasFocus': hasFocus,
     });
 
+    const contentStyle = {
+      whiteSpace: 'pre-wrap',
+    };
+
     return (
       <div className={className}>
         <div
           className={cx('public/DraftEditorPlaceholder/inner')}
-          id={this.props.accessibilityID}>
+          id={this.props.accessibilityID}
+          style={contentStyle}>
           {this.props.text}
         </div>
       </div>