Scale client area, hit test mask and bounds by device_scale_factor.

services/ui/demo/BUILD.gn

Index: services/ui/demo/BUILD.gn
diff --git a/services/ui/demo/BUILD.gn b/services/ui/demo/BUILD.gn
index 5a4e2bbb074e28e17efe7536cb369dba480c46a5..072da9f491bfb2434c40e3b64d9441987845e067 100644
--- a/services/ui/demo/BUILD.gn
+++ b/services/ui/demo/BUILD.gn
@@ -7,6 +7,8 @@ import("//services/service_manager/public/service_manifest.gni")
 import("//testing/test.gni")
 
 source_set("lib") {
+  testonly = true
+
   sources = [
     "bitmap_uploader.cc",
     "bitmap_uploader.h",
@@ -26,11 +28,14 @@ source_set("lib") {
     "//services/ui/public/cpp",
     "//services/ui/public/cpp:internal",
     "//services/ui/public/interfaces",
+    "//ui/display:test_support",
     "//ui/gfx/geometry",
   ]
 }
 
 service("mus_demo") {
+  testonly = true
+
   sources = [
     "main.cc",
   ]
@@ -79,6 +84,8 @@ test("mus_demo_unittests") {
 }
 
 group("demo") {
+  testonly = true
+
   deps = [
     ":mus_demo",
   ]