Add logging for slow device events, limit network UI update rate

ash/system/chromeos/network/tray_network_state_observer.h

 // Copyright (c) 2012 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 ASH_SYSTEM_CHROMEOS_NETWORK_TRAY_NETWORK_STATE_OBSERVER_H
 #define ASH_SYSTEM_CHROMEOS_NETWORK_TRAY_NETWORK_STATE_OBSERVER_H
 
 #include <string>
 
 #include "base/compiler_specific.h"
+#include "base/timer/timer.h"
 #include "chromeos/network/network_state_handler_observer.h"
 
 namespace ash {
 
 class TrayNetworkStateObserver : public chromeos::NetworkStateHandlerObserver {
  public:
   class Delegate {
    public:
-    // Called when the network state may have changed. If |list_changed| is
-    // true then the list of networks may have changed.
-    virtual void NetworkStateChanged(bool list_changed) = 0;
-
-    // Called when the properties for |network| may have been updated.
-    virtual void NetworkServiceChanged(
-        const chromeos::NetworkState* network) = 0;
+    // Called when any interesting network changes occur. The frequency of this
+    // event is limited to kUpdateFrequencyMs.
+    virtual void NetworkStateChanged() = 0;
 
    protected:
     virtual ~Delegate() {}
   };
 
   explicit TrayNetworkStateObserver(Delegate* delegate);
 
-  virtual ~TrayNetworkStateObserver();
+  ~TrayNetworkStateObserver() override;
 
   // NetworkStateHandlerObserver overrides.
-  virtual void NetworkListChanged() override;
-  virtual void DeviceListChanged() override;
-  virtual void DefaultNetworkChanged(
+  void NetworkListChanged() override;
+  void DeviceListChanged() override;
+  void DefaultNetworkChanged(const chromeos::NetworkState* network) override;
+  void NetworkConnectionStateChanged(
       const chromeos::NetworkState* network) override;
-  virtual void NetworkConnectionStateChanged(
-      const chromeos::NetworkState* network) override;
-  virtual void NetworkPropertiesUpdated(
-      const chromeos::NetworkState* network) override;
+  void NetworkPropertiesUpdated(const chromeos::NetworkState* network) override;
 
  private:
   Delegate* delegate_;
+  bool purge_icons_;
+  base::OneShotTimer<TrayNetworkStateObserver> timer_;
+
+  void SignalUpdate();
+  void SendNetworkStateChanged();
 
   DISALLOW_COPY_AND_ASSIGN(TrayNetworkStateObserver);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_CHROMEOS_NETWORK_TRAY_NETWORK_STATE_OBSERVER_H