android: add ThumbnailCache

chrome/browser/android/thumbnail/lru_expiring_cache.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_ANDROID_THUMBNAIL_LRU_EXPIRING_CACHE_H_
+#define CHROME_BROWSER_ANDROID_THUMBNAIL_LRU_EXPIRING_CACHE_H_
+
+#include "net/base/linked_hash_map.h"
+
+template <class Key, class Value>
+class LRUExpiringCache {
+ private:
+  typedef linked_hash_map<Key, Value> LinkedHashMap;
+
+ public:
+  typedef typename LinkedHashMap::iterator iterator;
+
+  explicit LRUExpiringCache(size_t max_cache_size)
+      : max_cache_size_(max_cache_size) {}
+
+  ~LRUExpiringCache() {}
+
+  void Put(const Key& key, const Value& value) {
+    map_[key] = value;
+    EvictIfFull();
+  }
+
+  Value Get(const Key& key) {
+    iterator iter = map_.find(key);
+    if (iter != map_.end())
+      return iter->second;
+    return Value();
+  }
+
+  bool Contains(const Key& key) const {
+    return map_.find(key) != map_.end();
+  }
+
+  Value Remove(const Key& key) {
+    Value val = Get(key);
+    map_.erase(key);
+    return val;
+  }
+
+  void Clear() { map_.clear(); }
+
+  iterator begin() { return map_.begin(); }
+  iterator end() { return map_.end(); }
+  size_t MaximumCacheSize() const { return max_cache_size_; }
+  size_t size() const { return map_.size(); }
+
+ private:

[David Trainor- moved to gerrit, 2014/06/17 08:12:11]

DISALLOW_COPY_AND_ASSIGN

[powei, 2014/06/19 23:05:58]

Done.

+  void EvictIfFull() {
+    while (map_.size() > max_cache_size_) {
+      iterator it = map_.begin();

[David Trainor- moved to gerrit, 2014/06/17 08:12:11]

Just checking, is the cache supposed to expire based on insert ordering or query
ordering?  What does a LinkedHashMap do by default for begin()?

[powei, 2014/06/19 23:05:58]

LinkedHashMap is insertion ordered.  I think that's the same as the original
Java code IIRC.

+      map_.erase(it);
+    }
+  }
+
+  size_t max_cache_size_;
+  LinkedHashMap map_;
+};
+
+#endif  // CHROME_BROWSER_ANDROID_THUMBNAIL_LRU_EXPIRING_CACHE_H_