Handle links in tagged PDFs.

Most of the magic that connects PDF annotations for hyperlinks to their
corresponding struct tree node happens inside of Skia. All that's needed
in Chromium is to add the proper node type for a link.

Bug: 1100712
Change-Id: Ica08cd04bc9dcb00684af5eb299927353618d0a0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2278173Reviewed-by: Eric Seckler <eseckler@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786099}

headless/lib/headless_web_contents_browsertest.cc

@@ -544,6 +544,14 @@ const char kExpectedStructTreeJSON[] = R"({
             "type": "NonStruct"
          } ]
       } ]
+   }, {
+      "type": "Div",
+      "~children": [ {
+         "type": "Link",
+         "~children": [ {
+            "type": "NonStruct"
+         } ]
+      } ]
    }, {
       "type": "Table",
       "~children": [ {

headless/test/data/structured_doc.html

@@ -6,6 +6,9 @@
     <li>Item 1</li>
     <li>Item 2</li>
   </ul>
+  <div>
+    <a href="https://google.com/">Link to Google</a>
+  </div>
   <table>
     <tr>
       <th>Header 1</th>

printing/common/metafile_utils.cc

@@ -27,6 +27,7 @@ const char kPDFStructureTypeDocument[] = "Document";
 const char kPDFStructureTypeParagraph[] = "P";
 const char kPDFStructureTypeDiv[] = "Div";
 const char kPDFStructureTypeHeading[] = "H";
+const char kPDFStructureTypeLink[] = "Link";
 const char kPDFStructureTypeList[] = "L";
 const char kPDFStructureTypeListItemLabel[] = "Lbl";
 const char kPDFStructureTypeListItemBody[] = "LI";
@@ -109,6 +110,9 @@ bool RecursiveBuildStructureTree(const ui::AXNode* ax_node,
       tag->fTypeString = GetHeadingStructureType(ax_node->GetIntAttribute(
           ax::mojom::IntAttribute::kHierarchicalLevel));
       break;
+    case ax::mojom::Role::kLink:
+      tag->fTypeString = kPDFStructureTypeLink;
+      break;
     case ax::mojom::Role::kList:
       tag->fTypeString = kPDFStructureTypeList;
       break;