Implements a display scale tray setting behind a chrome switch

ui/display/display_unittest.cc

Index: ui/display/display_unittest.cc
diff --git a/ui/display/display_unittest.cc b/ui/display/display_unittest.cc
index dee754b4d96ecee7153a82b64290f65decd9c0b9..aa0b55d5212cd47c1d47d58543c7f9ef364eb4e1 100644
--- a/ui/display/display_unittest.cc
+++ b/ui/display/display_unittest.cc
@@ -64,6 +64,13 @@ TEST(DisplayTest, ForcedDeviceScaleFactorByCommandLine) {
   Display::ResetForceDeviceScaleFactorForTesting();
 }
 
+TEST(DisplayTest, ForcedDeviceScaleFactor) {
+  Display::SetForceDeviceScaleFactor(2);
+
+  EXPECT_EQ(2, Display::GetForcedDeviceScaleFactor());
+  Display::ResetForceDeviceScaleFactorForTesting();
+}
+
 TEST(DisplayTest, DisplayHDRValues) {
   base::test::ScopedCommandLine scoped_command_line;
   base::CommandLine* command_line = scoped_command_line.GetProcessCommandLine();