[ObjC ARC] Converts ios/chrome/common/app_group to ARC

ios/chrome/common/app_group/BUILD.gn

Index: ios/chrome/common/app_group/BUILD.gn
diff --git a/ios/chrome/common/app_group/BUILD.gn b/ios/chrome/common/app_group/BUILD.gn
index 735962e478353d3038d3ce5a9fdf3db881071281..425245ba0fe5a8152a58003e018af3dd70157023 100644
--- a/ios/chrome/common/app_group/BUILD.gn
+++ b/ios/chrome/common/app_group/BUILD.gn
@@ -12,6 +12,8 @@ source_set("app_group") {
     "app_group_metrics.mm",
   ]
 
+  configs += [ "//build/config/compiler:enable_arc" ]
+
   deps = [
     "//base",
     "//components/version_info",
@@ -28,6 +30,8 @@ source_set("client") {
     "app_group_metrics_client.mm",
   ]
 
+  configs += [ "//build/config/compiler:enable_arc" ]
+
   deps = [
     ":app_group",
     "//base",
@@ -40,6 +44,8 @@ source_set("main_app") {
     "app_group_metrics_mainapp.mm",
   ]
 
+  configs += [ "//build/config/compiler:enable_arc" ]
+
   deps = [
     ":app_group",
     "//base",