Use WeakPtr in VersionUpdaterCros for safety

chrome/browser/ui/webui/help/version_updater_chromeos.h

Index: chrome/browser/ui/webui/help/version_updater_chromeos.h
diff --git a/chrome/browser/ui/webui/help/version_updater_chromeos.h b/chrome/browser/ui/webui/help/version_updater_chromeos.h
index aed47c7d2ff2213a820a20d41f4a0c9046680c7d..dca7c6bc5f7d24bdbd2c65681653a5ec2572beb1 100644
--- a/chrome/browser/ui/webui/help/version_updater_chromeos.h
+++ b/chrome/browser/ui/webui/help/version_updater_chromeos.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include "base/compiler_specific.h"
+#include "base/memory/weak_ptr.h"
 #include "chrome/browser/ui/webui/help/version_updater.h"
 #include "chromeos/dbus/update_engine_client.h"
 
@@ -43,6 +44,8 @@ class VersionUpdaterCros : public VersionUpdater,
   // Callback used to communicate current channel to the client.
   ChannelCallback channel_callback_;
 
+  base::WeakPtrFactory<VersionUpdaterCros> weak_ptr_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(VersionUpdaterCros);
 };