gpu: Add a couple of unit-tests for GpuService.

services/ui/gpu/BUILD.gn

Index: services/ui/gpu/BUILD.gn
diff --git a/services/ui/gpu/BUILD.gn b/services/ui/gpu/BUILD.gn
index c046f6f3cdc8cbe24069533e575dfe53937e0681..c735398ed4d22bfd3fa9f765cabd12bcf41b3452 100644
--- a/services/ui/gpu/BUILD.gn
+++ b/services/ui/gpu/BUILD.gn
@@ -51,12 +51,18 @@ test("mus_gpu_unittests") {
   deps = [
     ":gpu",
     "//base",
+    "//gpu",
     "//ipc",
     "//services/ui/common:run_all_service_tests",
+    "//services/ui/gpu/interfaces",
     "//testing/gtest",
     "//ui/gfx:memory_buffer",
     "//ui/gfx/geometry",
   ]
+
+  sources = [
+    "gpu_service_unittest.cc",
+  ]
 }
 
 service_manifest("mus_gpu_unittests_app_manifest") {