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) {
+    DCHECK(Contains(key));
+    iterator iter = map_.find(key);
+    return iter->second;
+  }
+
+  bool Contains(const Key& key) const {
+    return map_.find(key) != map_.end();
+  }
+
+  void Remove(const Key& key) {
+    map_.erase(key);
+  }
+
+  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:
+  void EvictIfFull() {
+    while (map_.size() > max_cache_size_) {
+      iterator it = map_.begin();
+      map_.erase(it);
+    }
+  }
+
+  size_t max_cache_size_;
+  LinkedHashMap map_;
+
+  DISALLOW_COPY_AND_ASSIGN(LRUExpiringCache);
+};
+
+#endif  // CHROME_BROWSER_ANDROID_THUMBNAIL_LRU_EXPIRING_CACHE_H_