Export stability metrics to UMA from Blimp engine

blimp/engine/BUILD.gn

Index: blimp/engine/BUILD.gn
diff --git a/blimp/engine/BUILD.gn b/blimp/engine/BUILD.gn
index 7869e8298c636bdf865e6c9c77cdc58acf34e58c..684035a9427c4a4d251e86774ca658a32fd92cdd 100644
--- a/blimp/engine/BUILD.gn
+++ b/blimp/engine/BUILD.gn
@@ -106,6 +106,8 @@ source_set("app_metrics") {
   sources = [
     "app/blimp_metrics_service_client.cc",
     "app/blimp_metrics_service_client.h",
+    "app/blimp_stability_metrics_provider.cc",
+    "app/blimp_stability_metrics_provider.h",
   ]
 
   public_deps = [
@@ -372,6 +374,7 @@ source_set("app_unit_tests") {
   sources = [
     "app/blimp_engine_config_unittest.cc",
     "app/blimp_metrics_service_client_unittest.cc",
+    "app/blimp_stability_metrics_provider_unittest.cc",
     "app/blimp_system_url_request_context_getter_unittest.cc",
     "app/settings_manager_unittest.cc",
     "app/ui/blimp_screen_unittest.cc",
@@ -392,6 +395,7 @@ source_set("app_unit_tests") {
     "//components/metrics:metrics",
     "//components/pref_registry:pref_registry",
     "//components/prefs:prefs",
+    "//components/prefs:test_support",
     "//content/test:test_support",
     "//net:test_support",
     "//testing/gmock",