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..72b29b4772209a244ad83c21cf7d3a44336d6dad
--- /dev/null
+++ b/net/nqe/network_qualities_manager.h
@@ -0,0 +1,69 @@
+// 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.

[RyanSturm, 2016/07/12 18:45:38]

Can you mention that it is LRU in this comment?

[tbansal1, 2016/07/12 19:40:18]

Done.

+class NET_EXPORT_PRIVATE NetworkQualitiesManager {
+ public:
+  NetworkQualitiesManager();
+  ~NetworkQualitiesManager();
+
+  // Adds the network quality |cached_network_quality| of network with id
+  // |network_id| to the cache.
+  void CacheNetworkQualityEstimate(
+      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_