Fix plural message that couldn't be extracted

BUG=623708
[email protected]

Review-Url: https://codereview.chromium.org/2108243002
Cr-Commit-Position: refs/heads/master@{#402958}
diff --git a/components/pdf_strings.grdp b/components/pdf_strings.grdp
index 572bef3..b0c7ff7 100644
--- a/components/pdf_strings.grdp
+++ b/components/pdf_strings.grdp
@@ -51,6 +51,7 @@
     </message>
     <message name="IDS_PDF_PAGE_INDEX" desc="Accessible label for each page, describing the page number">
       {COUNT, plural,
+         =1 {Page 1}
          other {Page #}}
     </message>
   </if>