Add a network quality cache observer

net/nqe/network_quality_store.h

 // 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_QUALITY_STORE_H_
 #define NET_NQE_NETWORK_QUALITY_STORE_H_
 
 #include <map>
 
 #include "base/macros.h"
+#include "base/observer_list.h"
 #include "base/threading/thread_checker.h"
 #include "net/base/net_export.h"
 #include "net/nqe/cached_network_quality.h"
+#include "net/nqe/effective_connection_type.h"
 #include "net/nqe/network_id.h"
 
 namespace net {
 
 namespace nqe {
 
 namespace internal {
 
 // NetworkQualityStore holds the network qualities of different networks in
 // memory. Entries are stored in LRU order, and older entries may be evicted.
 class NET_EXPORT_PRIVATE NetworkQualityStore {
  public:
+  // Observes changes in the cached network qualities.
+  class NET_EXPORT NetworkQualitiesCacheObserver {
+   public:
+    // Notifies the observer of a change in the cached network quality. The
+    // observer must register and unregister itself on the IO thread. All the
+    // observers would be notified on the IO thread. |network_id| is the ID of
+    // the network whose cached quality is being reported.
+    virtual void OnChangeInCachedNetworkQuality(
+        const nqe::internal::NetworkID& network_id,
+        const nqe::internal::CachedNetworkQuality& cached_network_quality) = 0;
+
+   protected:
+    NetworkQualitiesCacheObserver() {}
+    virtual ~NetworkQualitiesCacheObserver() {}
+
+   private:
+    DISALLOW_COPY_AND_ASSIGN(NetworkQualitiesCacheObserver);
+  };
+
   NetworkQualityStore();
   ~NetworkQualityStore();
 
   // Stores the network quality |cached_network_quality| of network with ID
   // |network_id|.
   void Add(const nqe::internal::NetworkID& network_id,
            const nqe::internal::CachedNetworkQuality& cached_network_quality);
 
   // Returns true if the network quality estimate was successfully read
   // for a network with ID |network_id|, and sets |cached_network_quality| to
   // the estimate read.
   bool GetById(const nqe::internal::NetworkID& network_id,
                nqe::internal::CachedNetworkQuality* cached_network_quality);
 
+  // Adds and removes |observer| from the list of cache observers.

[bengr, 2016/08/25 18:42:59]

Might be good to say that these are not threadsafe, if true, and that all
observers must live on the IO thread.

[tbansal1, 2016/08/25 20:31:07]

Done.

+  void AddNetworkQualitiesCacheObserver(
+      NetworkQualitiesCacheObserver* observer);
+  void RemoveNetworkQualitiesCacheObserver(
+      NetworkQualitiesCacheObserver* observer);
+
  private:
   // Maximum size of the store that holds network quality estimates.
   // A smaller size may reduce the cache hit rate due to frequent evictions.
   // A larger size may affect performance.
   static const size_t kMaximumNetworkQualityCacheSize = 10;
 
   // This does not use an unordered_map or hash_map for code simplicity (the 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;
 
   // Data structure that stores the qualities of networks.
   CachedNetworkQualities cached_network_qualities_;
 
+  // Observer list for changes in the cached network quality.
+  base::ObserverList<NetworkQualitiesCacheObserver>
+      network_qualities_cache_observer_list_;
+
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkQualityStore);
 };
 
 }  // namespace internal
 
 }  // namespace nqe
 
 }  // namespace net
 
 #endif  // NET_NQE_NETWORK_QUALITY_STORE_H_