[CrOS Tether] Create HostScanCache, which caches scan results and inserts them into the network sta…

chromeos/components/tether/tether_host_response_recorder.h

Index: chromeos/components/tether/tether_host_response_recorder.h
diff --git a/chromeos/components/tether/tether_host_response_recorder.h b/chromeos/components/tether/tether_host_response_recorder.h
index f87dd936ccc7777b3ef6aa67c41d0b0069739955..fed179e8c1dc0300fd5b6cb330452ddf5f00b9b9 100644
--- a/chromeos/components/tether/tether_host_response_recorder.h
+++ b/chromeos/components/tether/tether_host_response_recorder.h
@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "base/macros.h"
+#include "base/observer_list.h"
 #include "components/cryptauth/remote_device.h"
 
 class PrefService;
@@ -24,15 +25,23 @@ namespace tether {
 // Responses can be retrieved at a later time via getter methods.
 class TetherHostResponseRecorder {
  public:
-  // Note: The PrefService* passed here must be created using the same registry
-  // passed to RegisterPrefs().
-  TetherHostResponseRecorder(PrefService* pref_service);
-  virtual ~TetherHostResponseRecorder();
+  class Observer {
+   public:
+    virtual void OnPreviouslyConnectedHostIdsChanged() = 0;
+  };
 
   // Registers the prefs used by this class to |registry|. Must be called before
   // this class is utilized.
   static void RegisterPrefs(PrefRegistrySimple* registry);
 
+  // Note: The PrefService* passed here must be created using the same registry
+  // passed to RegisterPrefs().
+  explicit TetherHostResponseRecorder(PrefService* pref_service);
+  virtual ~TetherHostResponseRecorder();
+
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
   // Records a TetherAvailabilityResponse. This function should be called each
   // time that a response is received from a potential host, even if a
   // connection is not started.
@@ -60,12 +69,18 @@ class TetherHostResponseRecorder {
   virtual std::vector<std::string> GetPreviouslyConnectedHostIds() const;
 
  private:
-  void AddRecentResponse(const std::string& device_id,
+  friend class HostScanCacheTest;
+
+  void NotifyObserversPreviouslyConnectedHostIdsChanged();
+
+  // Returns whether the list was changed due to adding the response.
+  bool AddRecentResponse(const std::string& device_id,
                          const std::string& pref_name);
   std::vector<std::string> GetDeviceIdsForPref(
       const std::string& pref_name) const;
 
   PrefService* pref_service_;
+  base::ObserverList<Observer> observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(TetherHostResponseRecorder);
 };