Avoid to use environment.

scripts/slave/recipes/chromium_pgo.expected/full_tryserver_chromium_win_win_pgo.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\slave\\kill_processes.py"
     ],
     "name": "taskkill"
   },
   {
@@ skipping 194 matching lines @@
       "--gsutil-py-path",
       "RECIPE_PACKAGE_REPO[depot_tools]\\gsutil.py",
       "--ninja-path",
       "RECIPE_PACKAGE_REPO[depot_tools]\\ninja.exe",
       "--target",
       "Release",
       "--src-dir",
       "[SLAVE_BUILD]\\src",
       "--goma-cache-dir",
       "[GOMA_CACHE]",
+      "--buildbot-buildername",
+      "win_pgo",
+      "--buildbot-mastername",
+      "tryserver.chromium.win",
+      "--buildbot-slavename",
+      "TestSlavename",
       "--goma-fail-fast",
       "--goma-disable-local-fallback",
       "--",
       "chrome"
     ],
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "C:\\creds\\service_accounts\\service-account-goma-client.json",
       "PATH": "[SLAVE_BUILD]\\src\\out\\Release;%(PATH)s"
     },
     "name": "Compile: Instrumentation phase."
@@ skipping 480 matching lines @@
       "--gsutil-py-path",
       "RECIPE_PACKAGE_REPO[depot_tools]\\gsutil.py",
       "--ninja-path",
       "RECIPE_PACKAGE_REPO[depot_tools]\\ninja.exe",
       "--target",
       "Release",
       "--src-dir",
       "[SLAVE_BUILD]\\src",
       "--goma-cache-dir",
       "[GOMA_CACHE]",
+      "--buildbot-buildername",
+      "win_pgo",
+      "--buildbot-mastername",
+      "tryserver.chromium.win",
+      "--buildbot-slavename",
+      "TestSlavename",
       "--goma-fail-fast",
       "--goma-disable-local-fallback",
       "--",
       "chrome"
     ],
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "C:\\creds\\service_accounts\\service-account-goma-client.json"
     },
     "name": "Compile: Optimization phase."
   },
@@ skipping 22 matching lines @@
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"branch\": \"\", \"buildername\": \"win_pgo\", \"buildnumber\": 571, \"issue\": 12853011, \"mastername\": \"tryserver.chromium.win\", \"patch_project\": \"chromium\", \"patchset\": 1, \"project\": \"chrome\", \"recipe\": \"chromium_pgo\", \"repository\": \"\", \"requester\": \"commit-bot@chromium.org\", \"revision\": \"HEAD\", \"rietveld\": \"https://codereview.chromium.org\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}"
     ],
     "name": "package build"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]