Make enable_service_discovery a chrome/ feature.

tools/gn/docs/cookbook.md

 # GYP->GN Conversion Cookbook
 
 [TOC]
 
 ## Targets
 
 | *GYP*                                            | *GN*                                               |
 |:-------------------------------------------------|:---------------------------------------------------|
 | `'type': 'static_library', 'name': 'foo',`       | `static_library("foo") {` or `source_set("foo") {` |
 | `'type': 'shared_library', 'name': 'foo',`       | `shared_library("foo") {`                          |
@@ skipping 241 matching lines @@
 | `enable_hidpi` (0/1)                    | `enable_hidpi` (true/false)                    | `//ui/base/ui_features.gni`   |
 | `enable_managed_users` (0/1)            | `enable_managed_users` (true/false)            | `//build/config/features.gni` |
 | `enable_mdns` (0/1)                     | `enable_mdns` (true/false)                     | `//build/config/features.gni` |
 | `enable_one_click_signin` (0/1)         | `enable_one_click_signin` (true/false)         | `//chrome/common/features.gni` |
 | `enable_pepper_cdms` (0/1)              | `enable_pepper_cdms` (true/false)              | `//build/config/features.gni` |
 | `enable_plugins` (0/1)                  | `enable_plugins` (true/false)                  | `//build/config/features.gni` |
 | `enable_plugin_installation` (0/1)      | `enable_plugin_installation` (true/false)      | `//build/config/features.gni` |
 | `enable_basic_printing` (0/1)           | `enable_basic_printing` (true/false)           | `//build/config/features.gni` |
 | `enable_print_preview` (0/1)            | `enable_print_preview` (true/false)            | `//build/config/features.gni` |
 | `enable_rlz` (0/1)                      | `enable_rlz` (true/false)                      | `//build/config/features.gni` |
-| `enable_service_discovery` (0/1)        | `enable_service_discovery` (true/false)        | `//build/config/features.gni` |
 | `enable_spellcheck` (0/1)               | `enable_spellcheck` (true/false)               | `//build/config/features.gni` |
 | `enable_session_service` (0/1)          | `enable_session_service` (true/false)          | `//build/config/features.gni` |
 | `enable_task_manager` (0/1)             | `enable_task_manager` (true/false)             | `//build/config/features.gni` |
 | `enable_themes` (0/1)                   | `enable_themes` (true/false)                   | `//build/config/features.gni` |
 | `enable_webrtc` (0/1)                   | `enable_webrtc` (true/false)                   | `//build/config/features.gni` |
 | `image_loader_extension` (0/1)          | `enable_image_loader_extension` (true/false)   | `//build/config/features.gni` |
 | `input_speech` (0/1)                    | `enable_speech_input` (true/false)             | `//build/config/features.gni` |
 | `notifications` (0/1)                   | `enable_notifications` (true/false)            | `//build/config/features.gni` |
 | `ozone_platform_dri` (0/1)              | `ozone_platform_dri` (true/false)              | `//build/config/ui.gni`       |
 | `remoting` (0/1)                        | `enable_remoting` (true/false)                 | `//build/config/features.gni` |
@@ skipping 403 matching lines @@
 
 ```
 import("//mojo/public/tools/bindings/mojom.gni")
 
 mojom("mojo_bindings") {
   sources = [
     "foo.mojom",
   ]
 }
 ```