Factor out NetworkID and caching mechanism from n_q_e.{h,cc}

net/nqe/network_qualities_manager.h

Index: net/nqe/network_qualities_manager.h
diff --git a/net/nqe/network_qualities_manager.h b/net/nqe/network_qualities_manager.h
new file mode 100644
index 0000000000000000000000000000000000000000..18e89a9621a4be707e5ee89428f15380fe0513b7
--- /dev/null
+++ b/net/nqe/network_qualities_manager.h
@@ -0,0 +1,70 @@
+// Copyright 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_NQE_NETWORK_QUALITIES_MANAGER_H_
+#define NET_NQE_NETWORK_QUALITIES_MANAGER_H_
+
+#include <map>
+
+#include "base/macros.h"
+#include "base/threading/thread_checker.h"
+#include "net/base/net_export.h"
+#include "net/nqe/cached_network_quality.h"
+#include "net/nqe/network_id.h"
+
+namespace net {
+
+namespace nqe {
+
+namespace internal {
+
+// NetworkQualitiesManager holds the network qualities of different networks
+// in a cache which is backed up by memory. Entries are stored in LRU order, and
+// older entries may be evicted.
+class NET_EXPORT_PRIVATE NetworkQualitiesManager {

[bengr, 2016/07/21 00:16:24]

Hmm. Even if this will become a manager, I wonder if you shouldn't introduce a
store. It simplifies names:

class NetworkQualityStore {
  void Add(...);
  void GetById(...);
...

[tbansal1, 2016/07/21 01:25:39]

Done.

+ public:
+  NetworkQualitiesManager();
+  ~NetworkQualitiesManager();
+
+  // Adds the network quality |cached_network_quality| of network with id

[bengr, 2016/07/21 00:16:24]

Adds -> Stores

[tbansal1, 2016/07/21 01:25:39]

Done.

+  // |network_id| to the cache.

[bengr, 2016/07/21 00:16:24]

to the cache. -> .

[tbansal1, 2016/07/21 01:25:39]

Done.

+  void CacheNetworkQualityEstimate(

[bengr, 2016/07/21 00:16:24]

How about AddNetworkQualityEstimate or StoreNetworkQualityEstimate?

[tbansal1, 2016/07/21 01:25:40]

Obsolete.

+      const nqe::internal::NetworkID& network_id,
+      const nqe::internal::CachedNetworkQuality& cached_network_quality);
+
+  // Returns true if the cached network quality estimate was successfully read
+  // for network with id |network_id|, and sets |cached_network_quality| to the
+  // estimate read from the cache.
+  bool GetCachedNetworkQualityEstimate(
+      const nqe::internal::NetworkID& network_id,
+      nqe::internal::CachedNetworkQuality* cached_network_quality);
+
+ private:
+  // Maximum size of the cache that holds network quality estimates.
+  // Smaller size may reduce the cache hit rate due to frequent evictions.
+  // Larger size may affect performance.
+  static const size_t kMaximumNetworkQualityCacheSize = 10;
+
+  // This does not use a unordered_map or hash_map for code simplicity (key just
+  // implements operator<, rather than hash and equality) and because the map is
+  // tiny.
+  typedef std::map<nqe::internal::NetworkID,
+                   nqe::internal::CachedNetworkQuality>
+      CachedNetworkQualities;
+
+  // Cache that stores quality of previously seen networks.
+  CachedNetworkQualities cached_network_qualities_;
+
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(NetworkQualitiesManager);
+};
+
+}  // namespace internal
+
+}  // namespace nqe
+
+}  // namespace net
+
+#endif  // NET_NQE_NETWORK_QUALITIES_MANAGER_H_