Rename pdf-pane to viewer-pane

chrome/browser/resources/pdf/elements/pdf-pane/pdf-pane.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 /deep/ paper-dialog {
-  background-color: rgb(66, 66, 66);
-  color: rgb(250, 250, 250);
-  /* Since the pane slides in from the right, we want the scrollbar to be on
-   * the left. Setting direction to rtl achieves this.
-   */
-  direction: rtl;
-  font-family: Roboto, 'Helvetica Neue', Helvetica, Arial;
-  height: calc(100% - 64px);
-  margin: 0;
-  right: 0;
-  top: 64px;
-  width: 22em;
-}
-
-#reset-content {
-  direction: ltr;
-}
-
-:host /deep/ #scroller > h1 {
-  direction: ltr;
-  font-family: Roboto, 'Helvetica Neue', Helvetica, Arial;
-}
-
-hr {
-  background: rgb(66, 66, 66);
-  border: 0;
-  border-bottom: 1px dashed rgb(250, 250, 250);
-}