libyuv: Switch bots over to GN by default.

scripts/slave/recipes/libyuv/libyuv.expected/tryserver_libyuv_win.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\tools\\runit.py",
       "--show-path",
       "python",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\slave\\cleanup_temp.py"
     ],
@@ skipping 116 matching lines @@
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[depot_tools]\\gclient.py",
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]\\src",
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "C:\\creds\\service_accounts\\service-account-goma-client.json",
+      "GYP_CHROMIUM_NO_ACTION": "1",
       "GYP_DEFINES": "component=shared_library dcheck_always_on=1 fastbuild=1 gomadir='[CACHE]\\cipd\\goma' target_arch=ia32 use_goma=1",
       "PATH": "%(PATH)s;RECIPE_PACKAGE_REPO[depot_tools]"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
+      "RECIPE_PACKAGE_REPO[depot_tools]\\gn.py",
+      "--root=[SLAVE_BUILD]\\src",
+      "gen",
+      "//out/Debug",
+      "--args=symbol_level=2 dcheck_always_on=true is_debug=true target_cpu=\"x86\" use_goma=true goma_dir=\"[CACHE]\\cipd\\goma\""
+    ],
+    "cwd": "[SLAVE_BUILD]\\src",
+    "name": "gn"
+  },
+  {
+    "cmd": [
+      "python",
+      "-u",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\tools\\runit.py",
       "--show-path",
       "python",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\slave\\compile.py",
       "--gsutil-py-path",
       "RECIPE_PACKAGE_REPO[depot_tools]\\gsutil.py",
       "--ninja-path",
       "RECIPE_PACKAGE_REPO[depot_tools]\\ninja.exe",
       "--target",
       "Debug",
@@ skipping 12 matching lines @@
       "--compiler",
       "goma",
       "--goma-jsonstatus",
       "/path/to/tmp/json",
       "--goma-service-account-json-file",
       "C:\\creds\\service_accounts\\service-account-goma-client.json",
       "--goma-dir",
       "[CACHE]\\cipd\\goma",
       "--goma-fail-fast",
       "--goma-disable-local-fallback",
-      "--",
-      "All"
+      "--"
     ],
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "C:\\creds\\service_accounts\\service-account-goma-client.json"
     },
     "name": "compile",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output (invalid)@null@@@",
       "@@@STEP_LOG_END@json.output (invalid)@@@"
     ]
   },
@@ skipping 15 matching lines @@
       "libyuv_unittest.exe"
     ],
     "name": "libyuv_unittest"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]