Fix potential crashes in NetworkHandler code

chromeos/network/network_state_handler.cc

Index: chromeos/network/network_state_handler.cc
diff --git a/chromeos/network/network_state_handler.cc b/chromeos/network/network_state_handler.cc
index 5f4738a6cdfa0335e61aa025d72dfdf589114e36..6483446c0063942443f4a451536eb791b17aef41 100644
--- a/chromeos/network/network_state_handler.cc
+++ b/chromeos/network/network_state_handler.cc
@@ -71,11 +71,14 @@ NetworkStateHandler::NetworkStateHandler() : network_list_sorted_(false) {
 }
 
 NetworkStateHandler::~NetworkStateHandler() {
-  FOR_EACH_OBSERVER(NetworkStateHandlerObserver, observers_, IsShuttingDown());
   STLDeleteContainerPointers(network_list_.begin(), network_list_.end());
   STLDeleteContainerPointers(device_list_.begin(), device_list_.end());
 }
 
+void NetworkStateHandler::Shutdown() {
+  FOR_EACH_OBSERVER(NetworkStateHandlerObserver, observers_, IsShuttingDown());
+}
+
 void NetworkStateHandler::InitShillPropertyHandler() {
   shill_property_handler_.reset(new internal::ShillPropertyHandler(this));
   shill_property_handler_->Init();
@@ -92,20 +95,21 @@ void NetworkStateHandler::AddObserver(
     NetworkStateHandlerObserver* observer,
     const tracked_objects::Location& from_here) {
   observers_.AddObserver(observer);
-  device_event_log::AddEntry(from_here.file_name(), from_here.line_number(),
-                             device_event_log::LOG_TYPE_NETWORK,
-                             device_event_log::LOG_LEVEL_DEBUG,
-                             "NetworkStateHandler::AddObserver");
+  device_event_log::AddEntry(
+      from_here.file_name(), from_here.line_number(),
+      device_event_log::LOG_TYPE_NETWORK, device_event_log::LOG_LEVEL_DEBUG,
+      base::StringPrintf("NetworkStateHandler::AddObserver: 0x%p", observer));
 }
 
 void NetworkStateHandler::RemoveObserver(
     NetworkStateHandlerObserver* observer,
     const tracked_objects::Location& from_here) {
   observers_.RemoveObserver(observer);
-  device_event_log::AddEntry(from_here.file_name(), from_here.line_number(),
-                             device_event_log::LOG_TYPE_NETWORK,
-                             device_event_log::LOG_LEVEL_DEBUG,
-                             "NetworkStateHandler::RemoveObserver");
+  device_event_log::AddEntry(
+      from_here.file_name(), from_here.line_number(),
+      device_event_log::LOG_TYPE_NETWORK, device_event_log::LOG_LEVEL_DEBUG,
+      base::StringPrintf("NetworkStateHandler::RemoveObserver: 0x%p",
+                         observer));
 }
 
 NetworkStateHandler::TechnologyState NetworkStateHandler::GetTechnologyState(