Merge pull request mui#4250 from ToxicSalt/datepicker-classname

[DatePicker] Added className prop to DatePicker

src/DatePicker/DatePicker.js

@@ -23,6 +23,10 @@ class DatePicker extends Component {
      * Override the default text of the 'Cancel' button.
      */
     cancelLabel: PropTypes.node,
+    /**
+     * The css class name of the root element.
+     */
+    className: PropTypes.string,
     /**
      * Used to control how the Date Picker will be displayed when the input field is focused.
      * `dialog` (default) displays the DatePicker as a dialog with a modal.
@@ -251,6 +255,7 @@ class DatePicker extends Component {
       DateTimeFormat,
       autoOk,
       cancelLabel,
+      className,
       container,
       defaultDate, // eslint-disable-line no-unused-vars
       disableYearSelection,
@@ -275,7 +280,7 @@ class DatePicker extends Component {
     const formatDate = this.props.formatDate || this.formatDate;
 
     return (
-      <div style={prepareStyles(Object.assign({}, style))}>
+      <div className={className} style={prepareStyles(Object.assign({}, style))}>
         <TextField
           {...other}
           onFocus={this.handleFocus}