Let CrWinClang64(dbg) use gn.

scripts/slave/recipes/chromium.expected/full_chromium_fyi_CrWinClang64_dbg_.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\kill_processes.py"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "taskkill"
   },
@@ skipping 56 matching lines @@
       "@@@SET_BUILD_PROPERTY@got_v8_revision_cp@\"refs/heads/master@{#43426}\"@@@",
       "@@@SET_BUILD_PROPERTY@got_swarming_client_revision_cp@\"refs/heads/master@{#276089}\"@@@",
       "@@@SET_BUILD_PROPERTY@got_webrtc_revision_cp@\"refs/heads/master@{#120644}\"@@@",
       "@@@SET_BUILD_PROPERTY@got_revision_cp@\"refs/heads/master@{#170242}\"@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
-      "[SLAVE_BUILD]\\src\\tools\\swarming_client\\swarming.py",
-      "--version"
-    ],
-    "cwd": "[SLAVE_BUILD]",
-    "name": "swarming.py --version",
-    "stdout": "/path/to/tmp/",
-    "~followup_annotations": [
-      "@@@STEP_TEXT@0.4.10@@@"
-    ]
-  },
-  {
-    "cmd": [
-      "python",
-      "-u",
       "[DEPOT_TOOLS]\\gclient.py",
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]",
     "env": {
-      "GYP_DEFINES": "clang=1 component=shared_library fastbuild=1 target_arch=x64 test_isolation_mode=prepare"
+      "GYP_CHROMIUM_NO_ACTION": "1"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
+      "python",
+      "-u",
+      "[SLAVE_BUILD]\\src\\tools\\mb\\mb.py",
+      "gen",
+      "-v",
+      "-m",
+      "chromium.fyi",
+      "-b",
+      "CrWinClang64(dbg)",
+      "--config-file",
+      "[SLAVE_BUILD]\\src\\tools\\mb\\mb_config.pyl",
+      "--goma-dir",
+      "[BUILD]\\goma",
+      "//out/Debug_x64"
+    ],
+    "cwd": "[SLAVE_BUILD]",
+    "name": "generate_build_files"
+  },
+  {
+    "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "[SLAVE_BUILD]\\src\\testing\\buildbot\\chromium.fyi.json",
       "/path/to/tmp/json"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "read test spec",
     "~followup_annotations": [
       "@@@STEP_TEXT@path: [SLAVE_BUILD]\\src\\testing\\buildbot\\chromium.fyi.json@@@",
-      "@@@STEP_LOG_LINE@json.output@{@@@",
-      "@@@STEP_LOG_LINE@json.output@  \"CrWinClang64(dbg) tester\": {@@@",
-      "@@@STEP_LOG_LINE@json.output@    \"gtest_tests\": [@@@",
-      "@@@STEP_LOG_LINE@json.output@      {@@@",
-      "@@@STEP_LOG_LINE@json.output@        \"swarming\": {@@@",
-      "@@@STEP_LOG_LINE@json.output@          \"can_use_on_swarming_builders\": true@@@",
-      "@@@STEP_LOG_LINE@json.output@        }, @@@",
-      "@@@STEP_LOG_LINE@json.output@        \"test\": \"browser_tests\"@@@",
-      "@@@STEP_LOG_LINE@json.output@      }@@@",
-      "@@@STEP_LOG_LINE@json.output@    ]@@@",
-      "@@@STEP_LOG_LINE@json.output@  }@@@",
-      "@@@STEP_LOG_LINE@json.output@}@@@",
+      "@@@STEP_LOG_LINE@json.output@{}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]\\src\\testing\\scripts\\get_compile_targets.py",
       "--output",
       "/path/to/tmp/json",
@@ skipping 15 matching lines @@
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\cleanup_temp.py"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "cleanup_temp"
   },
   {
-    "cmd": [
-      "python",
-      "-u",
-      "RECIPE_MODULE[isolate]\\resources\\find_isolated_tests.py",
-      "--build-dir",
-      "[SLAVE_BUILD]\\src\\out\\Debug_x64",
-      "--clean-isolated-files"
-    ],
-    "cwd": "[SLAVE_BUILD]",
-    "name": "clean isolated files"
-  },
-  {
     "allow_subannotations": true,
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\clang_revision.py",
       "--src-dir",
       "[SLAVE_BUILD]\\src",
       "--output-json",
       "/path/to/tmp/json"
     ],
@@ skipping 18 matching lines @@
       "--build-tool",
       "ninja",
       "--compiler",
       "clang",
       "--"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "compile"
   },
   {
-    "cmd": [
-      "python",
-      "-u",
-      "RECIPE_MODULE[isolate]\\resources\\remove_build_metadata.py",
-      "--build-dir",
-      "[SLAVE_BUILD]\\src\\out\\Debug_x64",
-      "--src-dir",
-      "[SLAVE_BUILD]\\src"
-    ],
-    "cwd": "[SLAVE_BUILD]",
-    "name": "remove_build_metadata"
-  },
-  {
-    "cmd": [
-      "python",
-      "-u",
-      "RECIPE_MODULE[isolate]\\resources\\isolate.py",
-      "[SLAVE_BUILD]\\src\\tools\\swarming_client",
-      "batcharchive",
-      "--dump-json",
-      "/path/to/tmp/json",
-      "--isolate-server",
-      "https://isolateserver.appspot.com",
-      "--verbose",
-      "[SLAVE_BUILD]\\src\\out\\Debug_x64\\browser_tests.isolated.gen.json"
-    ],
-    "cwd": "[SLAVE_BUILD]",
-    "name": "isolate tests",
-    "~followup_annotations": [
-      "@@@STEP_LOG_LINE@json.output@{@@@",
-      "@@@STEP_LOG_LINE@json.output@  \"browser_tests\": \"[dummy hash for browser_tests]\"@@@",
-      "@@@STEP_LOG_LINE@json.output@}@@@",
-      "@@@STEP_LOG_END@json.output@@@"
-    ]
-  },
-  {
     "allow_subannotations": true,
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\zip_build.py",
       "--target",
       "Debug_x64",
       "--build-url",
       "gs://chromium-fyi-archive/chromium.fyi/CrWinClang64(dbg)",
       "--build_revision",
       "f27fede2220bcd326aee3e86ddfd4ebd0fe58cb9",
       "--factory-properties",
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"buildername\": \"CrWinClang64(dbg)\", \"buildnumber\": 571, \"mastername\": \"chromium.fyi\", \"parent_buildername\": null, \"recipe\": \"chromium\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}",
       "--build-properties",
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"buildername\": \"CrWinClang64(dbg)\", \"buildnumber\": 571, \"mastername\": \"chromium.fyi\", \"parent_buildername\": null, \"recipe\": \"chromium\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "package build"
   }
 ]