Stop to use contextmanager for goma.build_with_goma

scripts/slave/recipe_modules/goma/example.expected/mac_goma_disabled.json

 [
   {
     "cmd": [],
     "name": "ensure_goma"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::cipd]/resources/bootstrap.py",
@@ skipping 126 matching lines @@
       "GOMA_DUMP_STATS_FILE": "build_data_dir/goma_stats_proto",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "preprocess_for_goma.upload_goma_start_failed_logs",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@"
     ]
   },
   {
     "cmd": [
+      "python",
+      "-u",
+      "\nimport multiprocessing\nimport sys\n\njob_limit = 200\nif sys.platform.startswith('linux'):\n  # Use 80 for linux not to load goma backend.\n  job_limit = 80\n\ntry:\n  jobs = min(job_limit, multiprocessing.cpu_count() * 10)\nexcept NotImplementedError:\n  jobs = 50\n\nprint jobs\n"
+    ],
+    "name": "calculate the number of recommended jobs",
+    "stdout": "/path/to/tmp/",
+    "~followup_annotations": [
+      "@@@STEP_LOG_LINE@python.inline@@@@",
+      "@@@STEP_LOG_LINE@python.inline@import multiprocessing@@@",
+      "@@@STEP_LOG_LINE@python.inline@import sys@@@",
+      "@@@STEP_LOG_LINE@python.inline@@@@",
+      "@@@STEP_LOG_LINE@python.inline@job_limit = 200@@@",
+      "@@@STEP_LOG_LINE@python.inline@if sys.platform.startswith('linux'):@@@",
+      "@@@STEP_LOG_LINE@python.inline@  # Use 80 for linux not to load goma backend.@@@",
+      "@@@STEP_LOG_LINE@python.inline@  job_limit = 80@@@",
+      "@@@STEP_LOG_LINE@python.inline@@@@",
+      "@@@STEP_LOG_LINE@python.inline@try:@@@",
+      "@@@STEP_LOG_LINE@python.inline@  jobs = min(job_limit, multiprocessing.cpu_count() * 10)@@@",
+      "@@@STEP_LOG_LINE@python.inline@except NotImplementedError:@@@",
+      "@@@STEP_LOG_LINE@python.inline@  jobs = 50@@@",
+      "@@@STEP_LOG_LINE@python.inline@@@@",
+      "@@@STEP_LOG_LINE@python.inline@print jobs@@@",
+      "@@@STEP_LOG_END@python.inline@@@"
+    ]
+  },
+  {
+    "cmd": [
+      "echo",
+      "50"
+    ],
+    "name": "echo goma jobs"
+  },
+  {
+    "cmd": [
+      "echo",
+      "50"
+    ],
+    "name": "echo goma jobs second"
+  },
+  {
+    "cmd": [
       "ninja",
       "-C",
       "out/Release"
     ],
     "env": {
       "GOMA_DISABLED": "true"
     },
     "name": "ninja"
   },
   {
@@ skipping 33 matching lines @@
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "upload log goma start failed"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]