cache webpack_static helper to reduce json loading/parsing

https://github.com/mozilla/sumo-project/issues/874

kitsune/settings.py

@@ -413,6 +413,10 @@ STATICFILES_FINDERS = (
 
 STATICFILES_STORAGE = "django.contrib.staticfiles.storage.StaticFilesStorage"
 
+WEBPACK_LRU_CACHE = 128
+if DEV or TEST:
+    WEBPACK_LRU_CACHE = 0
+
 # Paths that don't require a locale prefix.
 SUPPORTED_NONLOCALES = (
     "1",

kitsune/sumo/utils.py

@@ -3,6 +3,7 @@ import re
 import sys
 from contextlib import contextmanager
 from datetime import datetime
+from functools import lru_cache
 
 from django.conf import settings
 from django.contrib.sites.models import Site
@@ -353,6 +354,7 @@ def check_for_spam_content(data):
     return is_toll_free or is_nanp_number or has_links
 
 
+@lru_cache(maxsize=settings.WEBPACK_LRU_CACHE)
 def webpack_static(source_path):
     """
     Get the URL for an asset processed by webpack.