Handle null Extension*s in AppRestoreService.

chrome/browser/extensions/app_restore_service.cc

Index: chrome/browser/extensions/app_restore_service.cc
diff --git a/chrome/browser/extensions/app_restore_service.cc b/chrome/browser/extensions/app_restore_service.cc
index bdb5a7cf3e3d47753ac316317de8a203ebc1afe2..6a91cc188f9aabfbb97f18a1240effc48a0edf8c 100644
--- a/chrome/browser/extensions/app_restore_service.cc
+++ b/chrome/browser/extensions/app_restore_service.cc
@@ -57,8 +57,9 @@ void AppRestoreService::Observe(int type,
   switch (type) {
     case chrome::NOTIFICATION_EXTENSION_HOST_DID_STOP_LOADING: {
       ExtensionHost* host = content::Details<ExtensionHost>(details).ptr();
-      if (host->extension()->is_platform_app()) {
-        RecordAppStart(host->extension()->id());
+      const Extension* extension = host->extension();
+      if (extension && extension->is_platform_app()) {
+        RecordAppStart(extension->id());
       }
       break;
     }