mus: Add views_mus_interactive_ui_tests target

ui/views/test/default_platform_test_helper.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 "base/memory/ptr_util.h"
 #include "ui/views/test/platform_test_helper.h"
 
 namespace views {
 namespace {
 
 class DefaultPlatformTestHelper : public PlatformTestHelper {
  public:
   DefaultPlatformTestHelper() {}
 
   ~DefaultPlatformTestHelper() override {}
 
-  bool IsMus() const override { return false; }
-
  private:
   DISALLOW_COPY_AND_ASSIGN(DefaultPlatformTestHelper);
 };
 
 }  // namespace
 
 // static
 std::unique_ptr<PlatformTestHelper> PlatformTestHelper::Create() {
   return base::WrapUnique(new DefaultPlatformTestHelper);
 }
 
+// static
+bool PlatformTestHelper::IsMus() {
+  return false;
+}
+
 }  // namespace views