PDFViewerUpdate: Add aria-label for bookmark expand icon.

Fixed: 1130478
Change-Id: I755023dbe5fc9c96b2e9c693a3b233b47551a9c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2439646
Commit-Queue: dpapad <dpapad@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812237}

chrome/browser/pdf/pdf_extension_util.cc

@@ -53,6 +53,7 @@ void AddPdfViewerStrings(base::Value* dict) {
   static constexpr webui::LocalizedString kPdfResources[] = {
     {"annotationsShowToggle", IDS_PDF_ANNOTATIONS_SHOW_TOGGLE},
     {"bookmarks", IDS_PDF_BOOKMARKS},
+    {"bookmarkExpandIconAriaLabel", IDS_PDF_BOOKMARK_EXPAND_ICON_ARIA_LABEL},
     {"downloadEdited", IDS_PDF_DOWNLOAD_EDITED},
     {"downloadOriginal", IDS_PDF_DOWNLOAD_ORIGINAL},
     {"labelPageNumber", IDS_PDF_LABEL_PAGE_NUMBER},

chrome/browser/resources/pdf/elements/viewer-bookmark.html

@@ -77,6 +77,7 @@
     <div id="item" on-click="onClick_">
       <div id="expand-container">
         <cr-icon-button id="expand" iron-icon="cr:chevron-right"
+            aria-label="$i18n{bookmarkExpandIconAriaLabel}"
             aria-expanded$="[[getAriaExpanded_(childrenShown_)]]"
             on-click="toggleChildren_"></cr-icon-button>
       </div>

components/pdf_strings.grdp

@@ -36,6 +36,9 @@
     <message name="IDS_PDF_BOOKMARKS" desc="Label for the bookmarks (table of contents) of a PDF document. Used as a heading for the bookmarks menu, and as a tooltip to open that menu">
       Bookmarks
     </message>
+    <message name="IDS_PDF_BOOKMARK_EXPAND_ICON_ARIA_LABEL" desc="aria-label describing the icon button that expands/collapses a bookmark entry that has children">
+      Section
+    </message>
 
     <message name="IDS_PDF_TOOLTIP_ROTATE_CW" desc="Button tooltip for the button which rotates a PDF document clockwise">
       Rotate clockwise

components/pdf_strings_grdp/IDS_PDF_BOOKMARK_EXPAND_ICON_ARIA_LABEL.png.sha1

+334500b8e86e8210fc32677b85db53a981344281
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