Downstream impact from https://codereview.chromium.org/1693993002/

scripts/slave/recipes/skia/ct_skps.expected/CT_DM_1m_SKPs.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE[depot_tools]/gclient.py",
       "config",
       "--spec",
       "cache_dir = None\nsolutions = [{'deps_file': 'DEPS', 'managed': True, 'name': 'skia', 'url': 'https://skia.googlesource.com/skia.git'}, {'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'url': 'https://chromium.googlesource.com/chromium/src.git'}]"
     ],
@@ skipping 70 matching lines @@
       "checkout",
       "-f",
       "FETCH_HEAD"
     ],
     "cwd": "[SLAVE_BUILD]/swarming.client",
     "name": "git checkout (swarming_client)"
   },
   {
     "cmd": [
       "git",
+      "rev-parse",
+      "HEAD"
+    ],
+    "cwd": "[SLAVE_BUILD]/swarming.client",
+    "name": "read revision",
+    "stdout": "/path/to/tmp/",
+    "~followup_annotations": [
+      "@@@STEP_TEXT@<br/>checked out 'deadbeef'<br/>@@@"
+    ]
+  },
+  {
+    "cmd": [
+      "git",
       "clean",
       "-f",
       "-d",
       "-x"
     ],
     "cwd": "[SLAVE_BUILD]/swarming.client",
     "name": "git clean (swarming_client)"
   },
   {
     "cmd": [
@@ skipping 1115 matching lines @@
       "@@@STEP_LOG_END@json.output@@@",
       "@@@STEP_LINK@shard #0 isolated out@blah@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]