Specify a default display UI scale to reset the zoom to

ash/display/root_window_transformers_unittest.cc

 // Copyright 2013 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/root_window_transformers.h"
 
 #include <memory>
 
 #include "ash/common/shelf/shelf_widget.h"
 #include "ash/display/display_manager.h"
@@ skipping 265 matching lines @@
   EXPECT_EQ("0,0 450x300", root_windows[0]->bounds().ToString());
   EXPECT_EQ("450,0 500x300", display2.bounds().ToString());
   EXPECT_EQ(1.5f, GetStoredUIScale(display1.id()));
   EXPECT_EQ(1.0f, GetStoredUIScale(display2.id()));
 
   ui::test::EventGenerator generator(root_windows[0]);
   generator.MoveMouseToInHost(500, 200);
   EXPECT_EQ("299,150", event_handler.GetLocationAndReset());
   magnifier->SetEnabled(false);
 
-  display_manager()->SetDisplayUIScale(display1.id(), 1.25f);
+  test::DisplayManagerTestApi(display_manager())
+      .SetDisplayUIScale(display1.id(), 1.25f);
   display1 = display::Screen::GetScreen()->GetPrimaryDisplay();
   display2 = display_manager()->GetSecondaryDisplay();
   magnifier->SetEnabled(true);
   EXPECT_EQ(2.0f, magnifier->GetScale());
   EXPECT_EQ("0,0 375x250", display1.bounds().ToString());
   EXPECT_EQ("0,0 375x250", root_windows[0]->bounds().ToString());
   EXPECT_EQ("375,0 500x300", display2.bounds().ToString());
   EXPECT_EQ(1.25f, GetStoredUIScale(display1.id()));
   EXPECT_EQ(1.0f, GetStoredUIScale(display2.id()));
   magnifier->SetEnabled(false);
@@ skipping 134 matching lines @@
   // Y margin must be margin is (500 - 500/400 * 200) / 2 = 125.
   EXPECT_EQ("0,125,0,125", transformer->GetHostInsets().ToString());
 
   UpdateDisplay("200x400,500x500");
   // The aspect ratio is flipped, so X margin is now 125.
   transformer = CreateCurrentRootWindowTransformerForMirroring();
   EXPECT_EQ("125,0,125,0", transformer->GetHostInsets().ToString());
 }
 
 }  // namespace ash