Revert of [Service Manager] Get rid of dynamic service discovery

services/service_manager/public/cpp/service.gni

Index: services/service_manager/public/cpp/service.gni
diff --git a/services/service_manager/public/cpp/service.gni b/services/service_manager/public/cpp/service.gni
index 6fce5888f010832aef616cf6f207eeb9515b6958..5846b1375740b8471b6c3950f8f50188a21632f2 100644
--- a/services/service_manager/public/cpp/service.gni
+++ b/services/service_manager/public/cpp/service.gni
@@ -3,19 +3,28 @@
 # found in the LICENSE file.
 
 import("//build/toolchain/toolchain.gni")
+import("//services/service_manager/public/constants.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
   import("//build/config/zip.gni")
 }
 
-# Generates a Service binary. The parameters of this template are those of an
-# executable.
+# Generates a Service "package", which includes:
+#
+#   - A self-named subdirectory
+#   - A binary .service executable
+#   - A resources subdirectory alongside the executable, which contains the
+#     contents of "resources"
+#
+# The parameters of this template are those of an executable
 template("service") {
   base_target_name = target_name
   if (defined(invoker.output_name)) {
     base_target_name = invoker.output_name
   }
+
+  final_target_name = target_name
 
   service_deps = []
   if (defined(invoker.deps)) {
@@ -25,19 +34,23 @@
   service_data_deps =
       [ "//services/service_manager/public/cpp/standalone_service:main" ]
 
+  if (defined(invoker.resources)) {
+    copy_step_name = "${base_target_name}__copy_resources"
+    copy(copy_step_name) {
+      sources = invoker.resources
+      outputs = [
+        "${root_out_dir}/${packages_directory}/${base_target_name}/resources/{{source_file_part}}",
+      ]
+      if (defined(invoker.testonly)) {
+        testonly = invoker.testonly
+      }
+      deps = service_deps
+    }
+    service_data_deps += [ ":$copy_step_name" ]
+  }
+
   if (defined(invoker.data_deps)) {
     service_data_deps += invoker.data_deps
-  }
-
-  if (defined(invoker.resources)) {
-    # TODO(rockot): Remove this once all existing service targets have stopped
-    # setting |resources|. This target serves no purpose other than to ensure
-    # that |resources| is actually used, avoiding GN complaints.
-    source_set("${target_name}__unused_resources_target") {
-      testonly = true
-      sources = invoker.resources
-      deps = invoker.deps
-    }
   }
 
   if (is_win) {
@@ -46,7 +59,10 @@
     executable_extension = "service"
   }
 
-  executable(target_name) {
+  executable_target_name = base_target_name + "_executable"
+  executable_name = base_target_name + "." + executable_extension
+
+  executable(executable_target_name) {
     output_name = base_target_name
     output_extension = executable_extension
 
@@ -120,4 +136,28 @@
       testonly = invoker.testonly
     }
   }
+
+  copy(final_target_name) {
+    forward_variables_from(invoker,
+                           [
+                             "testonly",
+                             "visibility",
+                           ])
+    deps = [
+      ":${executable_target_name}",
+    ]
+
+    # NOTE: We have to explicitly inherit the same data_deps as the executable
+    # target itself, rather than specifying a data depenedency on the executable
+    # target. This avoids needless duplication of service binary artifacts in
+    # test isolates, as the executable is unused in its original location.
+    data_deps = service_data_deps
+
+    sources = [
+      "${root_out_dir}/${executable_name}",
+    ]
+    outputs = [
+      "${root_out_dir}/${packages_directory}/${base_target_name}/${executable_name}",
+    ]
+  }
 }