Initially load new_tab.css with a timestamp for chrome://apps.

chrome/browser/resources/ntp4/new_tab.html

Index: chrome/browser/resources/ntp4/new_tab.html
diff --git a/chrome/browser/resources/ntp4/new_tab.html b/chrome/browser/resources/ntp4/new_tab.html
index 3ae53d5550673046fc9d2081fb77b4e530ba819e..513b4d268f008bf01a20e12caa3c78ed66ba5c26 100644
--- a/chrome/browser/resources/ntp4/new_tab.html
+++ b/chrome/browser/resources/ntp4/new_tab.html
@@ -28,8 +28,11 @@
 <link rel="stylesheet" href="nav_dot.css">
 <link rel="stylesheet" href="new_tab.css">
 <link rel="stylesheet" href="tile_page.css">
-<link id="themecss" rel="stylesheet" href="chrome://theme/css/new_tab_theme.css">

[Dan Beam, 2017/01/19 23:18:54]

maybe we could just use our new $i18n{} mechanism instead, i.e.

<link id="themecss" rel="stylesheet"
href="chrome://theme/css/new_tab_theme.css?$i18n{cacheBuster}">

and set a string in the C++ to a Date.now() equivalent (or anything that's
fairly random, really)

[rune, 2017/01/19 23:38:51]

Will that C++ string change on each load? I think it typically needs to.

-
+<script>
+// Until themes can clear the cache, force-reload the theme stylesheet.
+document.write('<link id="themecss" rel="stylesheet" ' +
+               'href="chrome://theme/css/new_tab_theme.css?' + Date.now() + '">');

[Dan Beam, 2017/01/21 02:05:56]

80 col wrap

+</script>

[Dan Beam, 2017/01/19 23:18:54]

i thought CSP prevented inline scripts from running. are you sure this works?

[rune, 2017/01/19 23:38:51]

Yes, it seems so. This is copied from incognito_tab.html, btw.

 <script src="../../../../ui/webui/resources/js/action_link.js"></script>
 <script src="../../../../ui/webui/resources/js/event_tracker.js"></script>
 <script src="../../../../ui/webui/resources/js/util.js"></script>