Add GetDisplayWithDisplayId to display::Screen.

ash/test/ash_test_base.cc

Index: ash/test/ash_test_base.cc
diff --git a/ash/test/ash_test_base.cc b/ash/test/ash_test_base.cc
index 128c2b9d43bc1ff0287883ac5a21c1282d07a942..20562512d14c9cb7aac85789574dca90d34bfb14 100644
--- a/ash/test/ash_test_base.cc
+++ b/ash/test/ash_test_base.cc
@@ -217,6 +217,12 @@ void AshTestBase::UpdateDisplay(const std::string& display_specs) {
       .UpdateDisplay(display_specs);
 }
 
+int64_t AshTestBase::SetFirstDisplayAsInternalDisplay() {
+  return display::test::DisplayManagerTestApi(
+             Shell::GetInstance()->display_manager())
+      .SetFirstDisplayAsInternalDisplay();
+}
+
 aura::Window* AshTestBase::CurrentContext() {
   return ash_test_helper_->CurrentContext();
 }