Unprefix flexbox properties in various CSS files

Source/core/Resources/pagepopups/calendarPicker.css

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 131 matching lines @@
     border-radius: 2px;
     position: absolute;
     padding: 10px;
     background-color: white;
     overflow: hidden;
     cursor: default;
 }
 
 .calendar-header-view {
     margin-bottom: 10px;
-    display: -webkit-flex;
-    -webkit-flex-flow: row;
+    display: flex;
+    flex-flow: row;
 }
 
 .calendar-title {
     -webkit-align-self: center;
-    -webkit-flex: 1;
+    flex: 1;
     text-align: left;
 }
 
 .rtl .calendar-title {
     text-align: right;
 }
 
 .month-popup-button,
 .month-popup-button:hover,
 .month-popup-button:disabled {
@@ skipping 63 matching lines @@
     -webkit-padding-start: 8px;
     background-color: #f5f5f5;
     border-bottom: 1px solid #bfbfbf;
 }
 
 .year-list-cell .month-chooser {
     padding: 0;
 }
 
 .month-buttons-row {
-    display: -webkit-flex;
+    display: flex;
 }
 
 .month-button {
-    -webkit-flex: 1;
+    flex: 1;
     height: 32px;
     padding: 0 !important;
     margin: 0 !important;
     background-image: none !important;
     background-color: #ffffff;
     border-width: 0 !important;
     box-shadow: none !important;
 }
 
 .month-button.highlighted {
@@ skipping 30 matching lines @@
 .year-list-view .scrubby-scroll-bar {
     right: 0;
 }
 
 .rtl .year-list-view .scrubby-scroll-bar {
     left: 0;
     right: auto;
     border-left-width: 0;
     border-right: 1px solid #bfbfbf;
 }