Add SystemProviderImpl

Also added support for running chromeos services unittests.
Added one simple unit test to exercise the setup.

Bug: 807015
Test: ninja -C out/ chromeos_services_unittests
Test: out/chromeos_services_unittests
Change-Id: If18b45115588493d35e0b2e354427aeaeb3f67a9
Reviewed-on: https://chromium-review.googlesource.com/922876
Commit-Queue: Xiaohui Chen <[email protected]>
Reviewed-by: Xiyuan Xia <[email protected]>
Reviewed-by: Dirk Pranke <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Cr-Commit-Position: refs/heads/master@{#538484}
diff --git a/BUILD.gn b/BUILD.gn
index 0be93385..1cb3ddca 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -375,6 +375,7 @@
       "//ash:ash_unittests",
       "//chromeos:chromeos_unittests",
       "//chromeos/components:chromeos_components_unittests",
+      "//chromeos/services:chromeos_services_unittests",
       "//components/session_manager/core",
       "//ui/app_list:app_list_demo",
       "//ui/app_list:app_list_unittests",