Add QuicLRUCache.

net/quic/platform/impl/quic_lru_cache_impl.h

+// Copyright (c) 2016 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 NET_QUIC_PLATFORM_IMPL_QUIC_LRU_CACHE_IMPL_H_
+#define NET_QUIC_PLATFORM_IMPL_QUIC_LRU_CACHE_IMPL_H_
+
+#include "base/containers/mru_cache.h"
+
+namespace net {
+
+template <class K, class V>
+class QuicLRUCacheImpl {
+ public:
+  explicit QuicLRUCacheImpl(int64_t total_units) : mru_cache_(total_units) {}
+
+  // Inserts one unit of |key|, |value| pair to the cache.
+  void Insert(const K& key, std::unique_ptr<V> value) {
+    mru_cache_.Put(key, *value);

[Ryan Hamilton, 2016/12/27 21:57:40]

Since value is dereferenced, but not released does value get deleted when the
unique_ptr is deleted?

[Ryan Hamilton, 2016/12/27 23:44:37]

Oh, I see. I misunderstood the type of the underlying mru_cache_. In that case,
can you make the value std::unique_ptr<V> instead?

  base::MRUCache<K, std::unique_ptr<V>> mru_cache_;

That would save a copy. In the case of the compressed certs cache, the V is
pretty huge so copying would be nice to avoid.

+  }
+
+  // If cache contains an entry for |key|, return a pointer to it.
+  // Else return nullptr.
+  V* Lookup(const K& key) {
+    auto cached_it = mru_cache_.Get(key);
+    if (cached_it != mru_cache_.end()) {
+      return &cached_it->second;
+    }
+    return nullptr;
+  }
+
+  // Removes all entries from the cache.
+  void Clear() { mru_cache_.Clear(); }
+
+  // Returns maximum size of the cache.
+  int64_t MaxSize() const { return mru_cache_.max_size(); }
+
+  // Returns current size of the cache.
+  int64_t Size() const { return mru_cache_.size(); }
+
+ private:
+  base::MRUCache<K, V> mru_cache_;
+
+  DISALLOW_COPY_AND_ASSIGN(QuicLRUCacheImpl);
+};
+
+}  // namespace net
+
+#endif  // NET_QUIC_PLATFORM_IMPL_QUIC_LRU_CACHE_IMPL_H_