Add and use a clang_linux asset.

infra/bots/recipes/swarm_trigger.expected/recipe_with_gerrit_patch.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport json\nimport sys\n\nwith open(sys.argv[1]) as f:\n  content = json.load(f)\n\nprint json.dumps(content, indent=2)\n",
       "{\"buildername\": \"Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Debug-Trybot\", \"buildnumber\": 5, \"event.change.number\": \"2100\", \"event.patchSet.ref\": \"refs/changes/00/2100/2\", \"mastername\": \"client.skia\", \"patch_storage\": \"gerrit\", \"path_config\": \"kitchen\", \"recipe\": \"swarm_trigger\", \"repository\": \"skia\", \"revision\": \"abc123\", \"slavename\": \"skiabot-linux-swarm-000\"}"
     ],
     "name": "print properties",
     "~followup_annotations": [
@@ skipping 243 matching lines @@
       "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "----",
       "help"
     ],
     "name": "gsutil help"
   },
   {
     "cmd": [
       "python",
       "-u",
+      "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
+      "[SLAVE_BUILD]/skia/infra/bots/assets/clang_linux/VERSION",
+      "/path/to/tmp/"
+    ],
+    "name": "read clang_linux VERSION"
+  },
+  {
+    "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]/swarming_temp_dir",
       "511"
     ],
     "name": "makedirs swarming tmp dir",
     "~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 85 matching lines @@
       "name:compile_skia",
       "--tag",
       "os:Ubuntu",
       "--tag",
       "revision:abc123",
       "--tag",
       "slavename:skiabot-linux-swarm-000",
       "--tag",
       "stepname:compile_skia on Ubuntu",
       "--idempotent",
+      "--cipd-package",
+      "clang_linux:skia/bots/clang_linux:version:0",
       "[dummy hash for compile_skia]",
       "--",
       "--workdir",
       "../../..",
       "swarm_compile",
       "event.change.number=2100",
       "repository=skia",
       "buildername=Build-Ubuntu-GCC-x86_64-Debug-Trybot",
       "mastername=client.skia.compile",
       "patch_storage=gerrit",
@@ skipping 434 matching lines @@
       "BOTO_CONFIG": "[HOME]/chromium-skia-gm.boto"
     },
     "name": "Upload DM Results"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]