Use JS Date().toLocaleDateString() to format date in header.

chrome/browser/resources/print_preview/print_preview_page.html

Index: chrome/browser/resources/print_preview/print_preview_page.html
diff --git a/chrome/browser/resources/print_preview/print_preview_page.html b/chrome/browser/resources/print_preview/print_preview_page.html
index 0eab31f0cd4f5e8a1f0e99b628afaafa4ffbbc05..aa765cd98531d81e308aa3e917c3ce02c68fa0e8 100644
--- a/chrome/browser/resources/print_preview/print_preview_page.html
+++ b/chrome/browser/resources/print_preview/print_preview_page.html
@@ -71,10 +71,12 @@ function setup(options) {
   header.style.height = pixels(options['topMargin']);
   content.style.height = pixels(options['height'] - options['topMargin'] -
                                 options['bottomMargin']);
-  footer.style.height = pixels(options['bottomMargin']);
-
-  document.querySelector('#date span').innerText = options['date'];
+  footer.style.height = pixels(options['bottomMargin']);
+
+  document.querySelector('#date span').innerText =
+      new Date(options['date'] * 1000).toLocaleDateString();
   document.querySelector('#title span').innerText = options['title'];
+
   document.querySelector('#url span').innerText = options['url'];
   document.querySelector('#page_number span').innerText = options['pageNumber'];