chromeos: Makes AshTestBase/Helper target mash when appropriate

ash/common/system/tray/tray_details_view_unittest.cc

 // Copyright 2013 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 "ash/common/system/tray/tray_details_view.h"
 
 #include "ash/common/ash_view_ids.h"
 #include "ash/common/system/tray/hover_highlight_view.h"
 #include "ash/common/system/tray/special_popup_row.h"
 #include "ash/common/system/tray/system_tray.h"
@@ skipping 108 matching lines @@
     tray->ShowDefaultView(BUBBLE_CREATE_NEW);
     RunAllPendingInMessageLoop();
     tray->ShowDetailedView(test_item, 0, true, BUBBLE_USE_EXISTING);
     RunAllPendingInMessageLoop();
 
     return test_item->detailed_view()->tray_popup_header_button();
   }
 
   void TransitionFromDetailedToDefaultView(TestDetailsView* detailed) {
     detailed->TransitionToDefaultView();
-    scoped_task_runner_->FastForwardBy(
-        base::TimeDelta::FromMilliseconds(kTrayDetailedViewTransitionDelayMs));
+    (*scoped_task_runner_)
+        ->FastForwardBy(base::TimeDelta::FromMilliseconds(
+            kTrayDetailedViewTransitionDelayMs));
   }
 
   void FocusBackButton(TestDetailsView* detailed) {
     detailed->back_button_->RequestFocus();
   }
 
+  void SetUp() override {
+    AshTestBase::SetUp();
+    scoped_task_runner_ =
+        base::MakeUnique<base::ScopedMockTimeMessageLoopTaskRunner>();
+  }
+
+  void TearDown() override {
+    scoped_task_runner_.reset();
+    AshTestBase::TearDown();
+  }
+
  private:
   // Used to control the |transition_delay_timer_|.
-  base::ScopedMockTimeMessageLoopTaskRunner scoped_task_runner_;
+  std::unique_ptr<base::ScopedMockTimeMessageLoopTaskRunner>
+      scoped_task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayDetailsViewTest);
 };
 
 TEST_F(TrayDetailsViewTest, TransitionToDefaultViewTest) {
   SystemTray* tray = GetPrimarySystemTray();
   ASSERT_TRUE(tray->GetWidget());
 
   TestItem* test_item_1 = new TestItem;
   TestItem* test_item_2 = new TestItem;
@@ skipping 76 matching lines @@
 
   // Sticky header layer should be above the last child's layer.
   EXPECT_EQ(3u, layers.size());
   EXPECT_EQ(view3->layer(), layers[0]);
   EXPECT_EQ(view4->layer(), layers[1]);
   EXPECT_EQ(view2->layer(), layers[2]);
 }
 
 }  // namespace test
 }  // namespace ash