WebRTC: Rename trybots and add compile-only configs.

scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_mac_compile_x64_rel.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "tryserver.webrtc",
       "--builder",
-      "mac_x64_gn_rel",
+      "mac_compile_x64_rel",
       "--slave",
       "slavename",
       "--spec",
       "cache_dir = None\nsolutions = [{'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'url': 'https://chromium.googlesource.com/external/webrtc'}, {'deps_file': 'DEPS', 'managed': True, 'name': 'webrtc-limited', 'url': 'https://chrome-internal.googlesource.com/chrome/deps/webrtc-limited'}]",
       "--root",
       "src",
       "--revision_mapping_file",
       "{\"src\": \"got_revision\"}",
       "--issue",
       "666666",
@@ skipping 47 matching lines @@
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]",
     "env": {
-      "GYP_CHROMIUM_NO_ACTION": "1",
       "GYP_DEFINES": "clang=1 component=static_library dcheck_always_on=1 fastbuild=1 gomadir='[BUILD]/goma' mac_sdk=10.9 target_arch=x64 use_goma=1"
     },
     "name": "gclient runhooks"
   },
   {
-    "cmd": [
-      "python",
-      "-u",
-      "[DEPOT_TOOLS]/gn.py",
-      "--root=[SLAVE_BUILD]/src",
-      "gen",
-      "//out/Release",
-      "--args=is_debug=false target_cpu=\"x64\" use_goma=true goma_dir=\"[BUILD]/goma\" build_with_chromium=false"
-    ],
-    "cwd": "[SLAVE_BUILD]",
-    "name": "gn"
-  },
-  {
     "allow_subannotations": true,
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/clang_revision.py",
       "--src-dir",
       "[SLAVE_BUILD]/src",
       "--output-json",
       "/path/to/tmp/json"
     ],
@@ skipping 17 matching lines @@
       "[SLAVE_BUILD]/src",
       "--build-tool",
       "ninja",
       "--compiler",
       "goma-clang",
       "--goma-dir",
       "[BUILD]/goma",
       "--goma-fail-fast",
       "--goma-disable-local-fallback",
       "--",
-      "all"
+      "All"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "compile"
   }
 ]