Switch the "Linux ChromiumOS Builder" to MB

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "chromium.chromiumos",
       "--builder",
       "Linux ChromiumOS Builder",
@@ skipping 115 matching lines @@
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[depot_tools]/gclient.py",
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]",
     "env": {
+      "GYP_CHROMIUM_NO_ACTION": "1",
       "GYP_DEFINES": "chromeos=1 component=static_library ffmpeg_branding=ChromeOS gomadir='[SLAVE_BUILD]/src/build/goma/client' proprietary_codecs=1 target_arch=x64 test_isolation_mode=prepare use_goma=1",
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]/src/testing/scripts/get_compile_targets.py",
@@ skipping 63 matching lines @@
       "[SLAVE_BUILD]/src/out/Release",
       "--clean-isolated-files"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "clean isolated files"
   },
   {
     "cmd": [
       "python",
       "-u",
+      "[SLAVE_BUILD]/src/tools/mb/mb.py",
+      "gen",
+      "-m",
+      "chromium.chromiumos",
+      "-b",
+      "Linux ChromiumOS Builder",
+      "--config-file",
+      "[SLAVE_BUILD]/src/tools/mb/mb_config.pyl",
+      "--goma-dir",
+      "[SLAVE_BUILD]/src/build/goma/client",
+      "--swarming-targets-file",
+      "browser_tests\n",
+      "//out/Release"
+    ],
+    "cwd": "[SLAVE_BUILD]",
+    "name": "generate_build_files",
+    "~followup_annotations": [
+      "@@@STEP_LOG_LINE@swarming-targets-file.txt@browser_tests@@@",
+      "@@@STEP_LOG_END@swarming-targets-file.txt@@@"
+    ]
+  },
+  {
+    "cmd": [
+      "python",
+      "-u",
       "RECIPE_PACKAGE_REPO[build]/scripts/tools/runit.py",
       "--show-path",
       "python",
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/compile.py",
       "--ninja-path",
       "RECIPE_PACKAGE_REPO[depot_tools]/ninja",
       "--target",
       "Release",
       "--src-dir",
       "[SLAVE_BUILD]/src",
@@ skipping 105 matching lines @@
     "~followup_annotations": [
       "@@@STEP_TEXT@Linux ChromiumOS Tests (1)@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]