V8: Switch on MB on older branches

scripts/slave/recipes/v8.expected/full_client_dynamorio_linux_v8_dr.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "client.dynamorio",
       "--builder",
       "linux-v8-dr",
@@ skipping 106 matching lines @@
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[depot_tools]/gclient.py",
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]/v8",
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
+      "GYP_CHROMIUM_NO_ACTION": "1",
       "GYP_DEFINES": "gomadir='[CACHE]/cipd/goma' target_arch=x64 use_goma=1 v8_target_arch=x64",
       "GYP_GENERATORS": "ninja",
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]/scripts/tools/runit.py",
       "--show-path",
       "python",
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/cleanup_temp.py"
     ],
     "name": "cleanup_temp"
   },
   {
     "cmd": [
       "python",
       "-u",
+      "[SLAVE_BUILD]/v8/tools/mb/mb.py",
+      "gen",
+      "-m",
+      "client.dynamorio",
+      "-b",
+      "linux-v8-dr",
+      "--config-file",
+      "[SLAVE_BUILD]/v8/infra/mb/mb_config.pyl",
+      "--goma-dir",
+      "[CACHE]/cipd/goma",
+      "--gyp-script=gypfiles/gyp_v8",
+      "//out/Release"
+    ],
+    "cwd": "[SLAVE_BUILD]/v8",
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
+    },
+    "name": "generate_build_files",
+    "stdout": "/path/to/tmp/",
+    "~followup_annotations": [
+      "@@@STEP_LOG_LINE@stdout@some line@@@",
+      "@@@STEP_LOG_LINE@stdout@GYP_DEFINES='target_arch=x64 cool_flag=a=1'@@@",
+      "@@@STEP_LOG_LINE@stdout@moar@@@",
+      "@@@STEP_LOG_END@stdout@@@"
+    ]
+  },
+  {
+    "cmd": [
+      "python",
+      "-u",
       "\nimport sys, os\npath = sys.argv[1]\nmode = int(sys.argv[2])\nif not os.path.isdir(path):\n  if os.path.exists(path):\n    print \"%s exists but is not a dir\" % path\n    sys.exit(1)\n  os.makedirs(path, mode)\n",
       "[SLAVE_BUILD]/v8/out/gn",
       "511"
     ],
     "name": "makedirs for peeking gn",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@python.inline@@@@",
       "@@@STEP_LOG_LINE@python.inline@import sys, os@@@",
       "@@@STEP_LOG_LINE@python.inline@path = sys.argv[1]@@@",
       "@@@STEP_LOG_LINE@python.inline@mode = int(sys.argv[2])@@@",
@@ skipping 181 matching lines @@
       "@@@STEP_LOG_LINE@durations@Duration: 00:00:101@@@",
       "@@@STEP_LOG_END@durations@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]