diff -r 000000000000 -r 6474c204b198 mobile/android/base/util/NonEvictingLruCache.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/base/util/NonEvictingLruCache.java	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,44 @@
+/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.gecko.util;
+
+import android.support.v4.util.LruCache;
+
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * An LruCache that also supports a set of items that will never be evicted.
+ *
+ * Alas, LruCache is final, so we compose rather than inherit.
+ */
+public class NonEvictingLruCache<K, V> {
+    private final ConcurrentHashMap<K, V> permanent = new ConcurrentHashMap<K, V>();
+    private final LruCache<K, V> evictable;
+
+    public NonEvictingLruCache(final int evictableSize) {
+        evictable = new LruCache<K, V>(evictableSize);
+    }
+
+    public V get(K key) {
+        V val = permanent.get(key);
+        if (val == null) {
+            return evictable.get(key);
+        }
+        return val;
+    }
+
+    public void putWithoutEviction(K key, V value) {
+        permanent.put(key, value);
+    }
+
+    public void put(K key, V value) {
+        evictable.put(key, value);
+    }
+
+    public void evictAll() {
+        evictable.evictAll();
+    }
+}