Tether: only scan when asked to by NetworkStateHandler.

chromeos/components/tether/host_scanner.h

Index: chromeos/components/tether/host_scanner.h
diff --git a/chromeos/components/tether/host_scanner.h b/chromeos/components/tether/host_scanner.h
index 85e1ef77c9fdaeaff8c6e99fa0a76c0a99b1cc38..7de4e1c37be615877cff704dba308139f8f7e15b 100644
--- a/chromeos/components/tether/host_scanner.h
+++ b/chromeos/components/tether/host_scanner.h
@@ -8,6 +8,9 @@
 #include <vector>
 
 #include "base/memory/weak_ptr.h"
+#include "base/observer_list.h"
+#include "base/time/clock.h"
+#include "base/time/time.h"
 #include "chromeos/components/tether/host_scanner_operation.h"
 #include "chromeos/components/tether/notification_presenter.h"
 #include "chromeos/network/network_state_handler.h"
@@ -27,34 +30,51 @@ class TetherHostResponseRecorder;
 // Scans for nearby tether hosts. When StartScan() is called, this class creates
 // a new HostScannerOperation and uses it to contact nearby devices to query
 // whether they can provide tether capabilities. Once the scan results are
-// received, they are stored in the HostScanCache passed to the constructor.
+// received, they are stored in the HostScanCache passed to the constructor,
+// and observers are notified via HostScanner::Observer::ScanFinished().
 class HostScanner : public HostScannerOperation::Observer {
  public:
+  class Observer {
+   public:
+    void virtual ScanFinished() = 0;
+  };
+
   HostScanner(TetherHostFetcher* tether_host_fetcher,
               BleConnectionManager* connection_manager,
               HostScanDevicePrioritizer* host_scan_device_prioritizer,
               TetherHostResponseRecorder* tether_host_response_recorder,
               NotificationPresenter* notification_presenter,
               DeviceIdTetherNetworkGuidMap* device_id_tether_network_guid_map,
-              HostScanCache* host_scan_cache);
+              HostScanCache* host_scan_cache,
+              base::Clock* clock);
   virtual ~HostScanner();
 
-  // Starts a host scan if there is no current scan. If a scan is ongoing, this
+  // Returns true if a scan is currently in progress.
+  virtual bool IsScanActive();
+
+  // Returns true if a scan has occurred recently within a timespan, determined
+  // by HostScanCache::kNumMinutesBeforeCacheEntryExpires.
+  virtual bool HasRecentlyScanned();
+
+  // Starts a host scan if there is no current scan. If a scan is active, this
   // function is a no-op.
   virtual void StartScan();
 
-  bool IsScanActive();
-
   // HostScannerOperation::Observer:
   void OnTetherAvailabilityResponse(
       std::vector<HostScannerOperation::ScannedDeviceInfo>&
           scanned_device_list_so_far,
       bool is_final_scan_result) override;
 
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
  private:
   friend class HostScannerTest;
   friend class HostScanSchedulerTest;
 
+  void NotifyScanFinished();
+
   void OnTetherHostsFetched(const cryptauth::RemoteDeviceList& tether_hosts);
   void SetCacheEntry(
       const HostScannerOperation::ScannedDeviceInfo& scanned_device_info);
@@ -66,10 +86,13 @@ class HostScanner : public HostScannerOperation::Observer {
   NotificationPresenter* notification_presenter_;
   DeviceIdTetherNetworkGuidMap* device_id_tether_network_guid_map_;
   HostScanCache* host_scan_cache_;
+  base::Clock* clock_;
 
   bool is_fetching_hosts_;
   std::unique_ptr<HostScannerOperation> host_scanner_operation_;
+  base::Time previous_scan_time_;
 
+  base::ObserverList<Observer> observer_list_;
   base::WeakPtrFactory<HostScanner> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(HostScanner);