demo of step.context bot_update issue

scripts/slave/recipes/blink_downstream.expected/webkit_tests_unexpected_error.json

 [
   {
     "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",
       "[BUILDER_CACHE]/V8_Blink_Linux_64",
       "511"
     ],
     "name": "makedirs checkout path",
@@ skipping 176 matching lines @@
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[depot_tools]/gclient.py",
       "runhooks"
     ],
-    "cwd": "[BUILDER_CACHE]/V8_Blink_Linux_64/src",
+    "cwd": "[SLAVE_BUILD]/src",
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
       "GYP_CHROMIUM_NO_ACTION": "1",
       "GYP_DEFINES": "component=static_library gomadir='[CACHE]/cipd/goma' target_arch=x64 use_goma=1",
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
-      "[BUILDER_CACHE]/V8_Blink_Linux_64/src/tools/mb/mb.py",
+      "[SLAVE_BUILD]/src/tools/mb/mb.py",
       "gen",
       "-m",
       "client.v8.fyi",
       "-b",
       "V8-Blink Linux 64",
       "--config-file",
-      "[BUILDER_CACHE]/V8_Blink_Linux_64/src/tools/mb/mb_config.pyl",
+      "[SLAVE_BUILD]/src/tools/mb/mb_config.pyl",
       "--goma-dir",
       "[CACHE]/cipd/goma",
       "//out/Release"
     ],
-    "cwd": "[BUILDER_CACHE]/V8_Blink_Linux_64/src",
+    "cwd": "[SLAVE_BUILD]/src",
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "generate_build_files (with patch)"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]/scripts/tools/runit.py",
       "--show-path",
       "python",
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/compile.py",
       "--gsutil-py-path",
       "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "--ninja-path",
       "RECIPE_PACKAGE_REPO[depot_tools]/ninja",
       "--target",
       "Release",
       "--src-dir",
-      "[BUILDER_CACHE]/V8_Blink_Linux_64/src",
+      "[SLAVE_BUILD]/src",
       "--goma-cache-dir",
       "[GOMA_CACHE]",
       "--goma-deps-cache-dir",
       "[GOMA_DEPS_CACHE]",
       "--compiler",
       "goma",
       "--goma-jsonstatus",
       "/path/to/tmp/json",
       "--goma-service-account-json-file",
       "/creds/service_accounts/service-account-goma-client.json",
@@ skipping 49 matching lines @@
       "--builder-name=V8-Blink Linux 64",
       "--slave-name=TestSlavename",
       "--build-number=571",
       "--run-python-script",
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/chromium/layout_test_wrapper.py",
       "--target",
       "Release",
       "-o",
       "[SLAVE_BUILD]/layout-test-results",
       "--build-dir",
-      "[BUILDER_CACHE]/V8_Blink_Linux_64/src/out",
+      "[SLAVE_BUILD]/src/out",
       "--json-test-results",
       "/path/to/tmp/json",
       "--test-results-server",
       "test-results.appspot.com",
       "--build-number",
       "571",
       "--builder-name",
       "V8-Blink Linux 64",
       "--step-name",
       "webkit_tests (with patch)",
       "--no-pixel-tests",
       "--additional-expectations",
-      "[BUILDER_CACHE]/V8_Blink_Linux_64/src/v8/tools/blink_tests/TestExpectations"
+      "[SLAVE_BUILD]/src/v8/tools/blink_tests/TestExpectations"
     ],
     "cwd": "[BUILDER_CACHE]/V8_Blink_Linux_64",
     "name": "webkit_tests (with patch)",
     "~followup_annotations": [
       "step returned non-zero exit code: 255",
       "@@@STEP_TEXT@<br/>unexpected_flakes:<br/>flake/slow.html<br/>flake/totally-flakey.html<br/>flake/timeout-then-crash.html<br/><br/>unexpected_failures:<br/>bad/totally-bad-probably.html<br/>tricky/totally-maybe-not-awesome.html<br/><br/>Total executed: 9001<br/>@@@",
       "@@@STEP_FAILURE@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/chromium/archive_layout_test_results.py",
       "--results-dir",
       "[SLAVE_BUILD]/layout-test-results",
       "--build-dir",
-      "[BUILDER_CACHE]/V8_Blink_Linux_64/src/out",
+      "[SLAVE_BUILD]/src/out",
       "--build-number",
       "571",
       "--builder-name",
       "V8-Blink Linux 64",
       "--gs-bucket",
       "gs://chromium-layout-test-archives",
       "--staging-dir",
       "[CACHE]/chrome_staging"
     ],
     "cwd": "[BUILDER_CACHE]/V8_Blink_Linux_64",
@@ skipping 17 matching lines @@
       "@@@STEP_FAILURE@@@"
     ]
   },
   {
     "name": "$result",
     "reason": "1 out of 1 aggregated steps failed. Failures: Step('webkit_tests') failed with return_code 1",
     "recipe_result": null,
     "status_code": 1
   }
 ]