chromeos: turn on simplified display management for mash

ash/test/ash_test_helper.cc

Index: ash/test/ash_test_helper.cc
diff --git a/ash/test/ash_test_helper.cc b/ash/test/ash_test_helper.cc
index 5bc6bd0051bb0d94e2600623d1c2c670cf187430..93be6c3beb3e277bd7f5f6c67500c4b736eac1d5 100644
--- a/ash/test/ash_test_helper.cc
+++ b/ash/test/ash_test_helper.cc
@@ -181,7 +181,7 @@ void AshTestHelper::SetUp(bool start_session) {
     session_controller_client_->CreatePredefinedUserSessions(1);
 
   // TODO(sky): mash should use this too http://crbug.com/718860.

[msw, 2017/05/26 16:38:50]

q: leaving this for a later cleanup pass? (ok either way)

[sky, 2017/06/05 17:19:44]

Yes. After this lands and stays enabled for a day or so I plan a cleanup pass.

-  if (config_ != Config::MASH) {
+  if (Shell::ShouldEnableSimplifiedDisplayManagement()) {
     // Tests that change the display configuration generally don't care about
     // the notifications and the popup UI can interfere with things like
     // cursors.
@@ -313,7 +313,7 @@ void AshTestHelper::UpdateDisplayForMash(const std::string& display_spec) {
 }
 
 display::Display AshTestHelper::GetSecondaryDisplay() {
-  if (config_ != Config::MASH)
+  if (Shell::ShouldEnableSimplifiedDisplayManagement())
     return Shell::Get()->display_manager()->GetSecondaryDisplay();
 
   std::vector<RootWindowController*> roots = GetRootsOrderedByDisplayId();
@@ -352,7 +352,7 @@ void AshTestHelper::CreateMashWindowManager() {
       window_manager_app_->window_manager()->window_tree_client();
   window_tree_client_private_ =
       base::MakeUnique<aura::WindowTreeClientPrivate>(window_tree_client);
-  if (config_ == Config::MUS) {
+  if (Shell::ShouldEnableSimplifiedDisplayManagement(config_)) {
     window_tree_client_private_->CallOnConnect();
   } else {
     int next_x = 0;