Change order that objects are destroyed in Tether shutdown.

Previously, the NotificationPresenter was being explicitly destroyed before the NotificationRemover, causing a segfault. This CL corrects that bug.

Bug: 751192
Change-Id: I397c1a7d96ddf9a8721ae96716952055ee4e0c75
Reviewed-on: https://chromium-review.googlesource.com/596502
Commit-Queue: Leslie Watkins <lesliewatkins@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491428}

chrome/browser/chromeos/tether/tether_service.cc

@@ -143,12 +143,13 @@ void TetherService::Shutdown() {
   if (adapter_)
     adapter_->RemoveObserver(this);
   registrar_.RemoveAll();
-  notification_presenter_.reset();
 
   // Shut down the feature. Note that this does not change Tether's technology
   // state in NetworkStateHandler because doing so could cause visual jank just
   // as the user logs out.
   StopTetherIfNecessary();
+
+  notification_presenter_.reset();
 }
 
 void TetherService::SuspendImminent() {