Subreddit CSS: Dump permacache-based last modified system.

This system is only used when stylesheets are not hosted on S3. The new
system saves a completely unnecessary C* lookup and ditches one more
thing from the permacache.

r2/r2/controllers/front.py

@@ -401,6 +401,15 @@ class FrontController(RedditController, OAuth2ResourceController):
 
         if stylesheet_contents:
             c.allow_loggedin_cache = True
+
+            if c.site.stylesheet_modified:
+                self.abort_if_not_modified(
+                    c.site.stylesheet_modified,
+                    private=False,
+                    max_age=timedelta(days=7),
+                    must_revalidate=False,
+                )
+
             c.response_content_type = 'text/css'
             c.response.content =  stylesheet_contents
             if c.site.type == 'private':

r2/r2/models/subreddit.py

@@ -23,6 +23,7 @@
 from __future__ import with_statement
 
 import base64
+import datetime
 import hashlib
 
 from pylons import c, g
@@ -64,6 +65,7 @@ class Subreddit(Thing, Printable):
                      stylesheet_rtl = None,
                      stylesheet_contents = '',
                      stylesheet_hash     = '',
+                     stylesheet_modified = None,
                      firsttext = strings.firsttext,
                      header = None,
                      header_size = None,
@@ -386,13 +388,15 @@ class Subreddit(Thing, Printable):
                               )
 
                 self.stylesheet_contents = ""
+                self.stylesheet_modified = None
             else:
                 self.stylesheet_hash = hashlib.md5(minified).hexdigest()
                 self.stylesheet_contents = minified
-                set_last_modified(self, 'stylesheet_contents')
+                self.stylesheet_modified = datetime.datetime.now(g.tz)
         else:
             self.stylesheet_contents = ""
             self.stylesheet_hash = ""
+            self.stylesheet_modified = datetime.datetime.now(g.tz)
         self.stylesheet_contents_user = ""  # reads from wiki; ensure pg clean
         self._commit()