Material PDF: Support RTL languages

chrome/browser/resources/pdf/elements/viewer-toolbar-dropdown/viewer-toolbar-dropdown.css

 /* Copyright 2015 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file. */
 
 :host {
   display: inline-block;
-  text-align: left;
+  text-align: start;
 }
 
 #container {
   position: absolute;
 }
 
 paper-material {
   background-color: rgb(256, 256, 256);
   border-radius: 4px;
   overflow-y: hidden;
@@ skipping 11 matching lines @@
   cursor: pointer;
   display: inline-block;
 }
 
 #icon.open {
   background-color: rgb(25, 27, 29);
   border-radius: 4px;
 }
 
 #arrow {
-  margin-left: -12px;
-  padding-right: 4px;
+  -webkit-margin-start: -12px;
+  -webkit-padding-end: 4px;
 }
 
 h1 {
   border-bottom: 1px solid rgb(219, 219, 219);
   color: rgb(33, 33, 33);
   font-size: 77.8%;
   font-weight: 500;
   margin: 0;
   padding: 14px 28px;
 }