chromeos: makes more tests run in both mash and ash

ash/system/chromeos/power/tablet_power_button_controller_unittest.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 "ash/system/chromeos/power/tablet_power_button_controller.h"
 
 #include <memory>
 
 #include "ash/common/ash_switches.h"
 #include "ash/common/session/session_state_delegate.h"
@@ skipping 57 matching lines @@
         std::unique_ptr<base::TickClock>(tick_clock_));
     shell_delegate_ =
         static_cast<TestShellDelegate*>(WmShell::Get()->delegate());
     generator_ = &AshTestBase::GetEventGenerator();
     power_manager_client_->SendBrightnessChanged(kNonZeroBrightness, false);
     EXPECT_FALSE(GetBacklightsForcedOff());
   }
 
   void TearDown() override {
     generator_ = nullptr;
+    const bool is_mash = WmShell::Get()->IsRunningInMash();
     AshTestBase::TearDown();
-    chromeos::DBusThreadManager::Shutdown();
+    // Mash shuts down dbus after each test.
+    if (!is_mash)
+      chromeos::DBusThreadManager::Shutdown();
   }
 
  protected:
   void PressPowerButton() {
     tablet_controller_->OnPowerButtonEvent(true, base::TimeTicks::Now());
   }
 
   void ReleasePowerButton() {
     tablet_controller_->OnPowerButtonEvent(false, base::TimeTicks::Now());
   }
@@ skipping 379 matching lines @@
   // Test that after another long duration, backlights should be forced off.
   tick_clock_->Advance(base::TimeDelta::FromMilliseconds(800));
   power_manager_client_->SendPowerButtonEvent(true, tick_clock_->NowTicks());
   power_manager_client_->SendPowerButtonEvent(false, tick_clock_->NowTicks());
   power_manager_client_->SendBrightnessChanged(0, false);
   EXPECT_TRUE(GetBacklightsForcedOff());
 }
 
 }  // namespace test
 }  // namespace ash