Revert of chromeos: Makes mushrome use simplified display management

ash/mus/test/wm_test_base.cc

Index: ash/mus/test/wm_test_base.cc
diff --git a/ash/mus/test/wm_test_base.cc b/ash/mus/test/wm_test_base.cc
index eb0979fde201acb9403dec13f642dc4a8bceccf3..a7776391a73e1ad2b981c072ade8dd5252c83226 100644
--- a/ash/mus/test/wm_test_base.cc
+++ b/ash/mus/test/wm_test_base.cc
@@ -7,12 +7,10 @@
 #include <algorithm>
 #include <vector>
 
-#include "ash/display/window_tree_host_manager.h"
 #include "ash/mus/test/wm_test_helper.h"
 #include "ash/mus/top_level_window_factory.h"
 #include "ash/mus/window_manager.h"
 #include "ash/mus/window_manager_application.h"
-#include "ash/public/cpp/config.h"
 #include "ash/public/cpp/session_types.h"
 #include "ash/public/interfaces/session_controller.mojom.h"
 #include "ash/session/session_controller.h"
@@ -25,7 +23,6 @@
 #include "ui/aura/window.h"
 #include "ui/compositor/scoped_animation_duration_scale_mode.h"
 #include "ui/display/display.h"
-#include "ui/display/manager/display_manager.h"
 
 namespace ash {
 namespace mus {
@@ -76,26 +73,19 @@
 }
 
 aura::Window* WmTestBase::GetPrimaryRootWindow() {
-  return Shell::Get()->GetPrimaryRootWindow();
+  std::vector<RootWindowController*> roots =
+      test_helper_->GetRootsOrderedByDisplayId();
+  DCHECK(!roots.empty());
+  return roots[0]->GetRootWindow();
 }
 
 aura::Window* WmTestBase::GetSecondaryRootWindow() {
-  if (Shell::GetAshConfig() == Config::MUS) {
-    return Shell::Get()->window_tree_host_manager()->GetRootWindowForDisplayId(
-        GetSecondaryDisplay().id());
-  }
-
   std::vector<RootWindowController*> roots =
       test_helper_->GetRootsOrderedByDisplayId();
   return roots.size() < 2 ? nullptr : roots[1]->GetRootWindow();
 }
 
 display::Display WmTestBase::GetPrimaryDisplay() {
-  if (Shell::GetAshConfig() == Config::MUS) {
-    return display::Screen::GetScreen()->GetDisplayNearestWindow(
-        Shell::Get()->GetPrimaryRootWindow());
-  }
-
   std::vector<RootWindowController*> roots =
       test_helper_->GetRootsOrderedByDisplayId();
   DCHECK(!roots.empty());
@@ -103,9 +93,6 @@
 }
 
 display::Display WmTestBase::GetSecondaryDisplay() {
-  if (Shell::GetAshConfig() == Config::MUS)
-    return Shell::Get()->display_manager()->GetSecondaryDisplay();
-
   std::vector<RootWindowController*> roots =
       test_helper_->GetRootsOrderedByDisplayId();
   return roots.size() < 2 ? display::Display()