drive: Fix a DCHECK failure at shutdown after Drive is disabled

chrome/browser/chromeos/extensions/file_browser_event_router.cc

Index: chrome/browser/chromeos/extensions/file_browser_event_router.cc
diff --git a/chrome/browser/chromeos/extensions/file_browser_event_router.cc b/chrome/browser/chromeos/extensions/file_browser_event_router.cc
index 715ad8aa4c9afec8abba5c2232d05ffb1b47faa7..61bfd77776a57ac6ed2912a0d2231f30ef6295a1 100644
--- a/chrome/browser/chromeos/extensions/file_browser_event_router.cc
+++ b/chrome/browser/chromeos/extensions/file_browser_event_router.cc
@@ -558,7 +558,12 @@ void FileBrowserEventRouter::DispatchMountCompletedEvent(
     DiskMountManager::MountEvent event,
     chromeos::MountError error_code,
     const DiskMountManager::MountPointInfo& mount_info) {
-  if (!profile_ || mount_info.mount_type == chromeos::MOUNT_TYPE_INVALID) {
+  // profile_ is NULL if ShutdownOnUIThread() is called earlier. This can
+  // happen at shutdown.
+  if (!profile_)
+    return;
+
+  if (mount_info.mount_type == chromeos::MOUNT_TYPE_INVALID) {
     NOTREACHED();
     return;
   }