PDF Viewer: Fix bookmark text alignment on old PDF viewer

Fixed: 1131152
Change-Id: Idb6b22c002b87748da4a9248b54bb5d288de75f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2429226Reviewed-by: dpapad <dpapad@chromium.org>
Commit-Queue: dpapad <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811194}

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

     <style>
       #item {
-        align-items: flex-start;
+        align-items: center;
         cursor: pointer;
         display: flex;
         height: 30px;
@@ -9,6 +9,7 @@
       }
 
       :host-context([pdf-viewer-update-enabled]) #item {
+        align-items: flex-start;
         height: initial;
         padding: 5px 0;
       }