Fixes crash in ~ShellConnection

ui/views/mus/views_mus_test_suite.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/mus/views_mus_test_suite.h"
 
 #include <memory>
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
@@ skipping 67 matching lines @@
     // WindowManagerConnection cannot be created from here yet, although the
     // connector and identity are available at this point. This is because
     // WindowManagerConnection needs a ViewsDelegate and a MessageLoop to have
     // been installed first. So delay the creation until the necessary
     // dependencies have been met.
     PlatformTestHelper::set_factory(base::Bind(
         &CreatePlatformTestHelper, shell_connector_.get(), shell_identity_));
   }
 
   ~ShellConnection() {
-    views::WindowManagerConnection::Reset();
+    if (views::WindowManagerConnection::Exists())
+      views::WindowManagerConnection::Reset();
     base::WaitableEvent wait(false, false);
     thread_.task_runner()->PostTask(
         FROM_HERE, base::Bind(&ShellConnection::TearDownConnections,
                               base::Unretained(this), &wait));
     wait.Wait();
   }
 
  private:
   void SetUpConnections(base::WaitableEvent* wait) {
     background_shell_.reset(new shell::BackgroundShell);
@@ skipping 51 matching lines @@
   ViewsTestSuite::Initialize();
   shell_connections_.reset(new ShellConnection);
 }
 
 void ViewsMusTestSuite::Shutdown() {
   shell_connections_.reset();
   ViewsTestSuite::Shutdown();
 }
 
 }  // namespace views