Enable ash shell and unit tests in GN build.

ash/display/display_controller_unittest.cc

 // Copyright (c) 2012 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/display/display_controller.h"
 
 #include "ash/ash_switches.h"
 #include "ash/display/display_info.h"
 #include "ash/display/display_layout_store.h"
 #include "ash/display/display_manager.h"
@@ skipping 220 matching lines @@
   virtual void PreInit() OVERRIDE {
     Shell::GetInstance()->display_controller()->AddObserver(this);
   }
 
   // ash::DisplayController::Observer:
   virtual void OnDisplaysInitialized() OVERRIDE {
     DCHECK(!displays_initialized_);
     displays_initialized_ = true;
   }
 
-  const bool displays_initialized() const {
+  bool displays_initialized() const {
     return displays_initialized_;
   }
 
  private:
   bool displays_initialized_;
 
   DISALLOW_COPY_AND_ASSIGN(StartupHelper);
 };
 
 class DisplayControllerStartupTest : public test::AshTestBase {
@@ skipping 1082 matching lines @@
   EXPECT_EQ("aura_root_x", GetXWindowName(secondary->GetHost()));
 
   // Switching back to single display.
   UpdateDisplay("300x400");
   EXPECT_EQ("aura_root_0", GetXWindowName(
       Shell::GetPrimaryRootWindow()->GetHost()));
 }
 #endif
 
 }  // namespace ash