Modify Skia recipes to allow running XSAN on Swarming.

scripts/slave/recipes/skia/swarm_test.expected/Test-Android-GCC-Nexus6-GPU-Adreno420-Arm7-Release.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]/skia/tools/buildbot_spec.py",
       "/path/to/tmp/json",
       "Test-Android-GCC-Nexus6-GPU-Adreno420-Arm7-Release"
     ],
     "cwd": "[SLAVE_BUILD]/skia",
@@ skipping 207 matching lines @@
       "SKIA_OUT": "[SLAVE_BUILD]/out"
     },
     "name": "read SK_IMAGE_VERSION",
     "stdout": "/path/to/tmp/"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport os, sys\nfrom common import chromium_utils # Error? See https://crbug.com/584783.\n\n\nif os.path.exists(sys.argv[1]):\n  chromium_utils.RemoveDirectory(sys.argv[1])\n",
-      "[SWARM_OUT_DIR]/dm"
+      "[CUSTOM_[SWARM_OUT_DIR]]/dm"
     ],
     "env": {
       "PYTHONPATH": "build/scripts"
     },
     "name": "rmtree dm",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@python.inline@@@@",
       "@@@STEP_LOG_LINE@python.inline@import os, sys@@@",
       "@@@STEP_LOG_LINE@python.inline@from common import chromium_utils # Error? See https://crbug.com/584783.@@@",
       "@@@STEP_LOG_LINE@python.inline@@@@",
       "@@@STEP_LOG_LINE@python.inline@@@@",
       "@@@STEP_LOG_LINE@python.inline@if os.path.exists(sys.argv[1]):@@@",
       "@@@STEP_LOG_LINE@python.inline@  chromium_utils.RemoveDirectory(sys.argv[1])@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "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",
-      "[SWARM_OUT_DIR]/dm",
+      "[CUSTOM_[SWARM_OUT_DIR]]/dm",
       "511"
     ],
     "name": "makedirs dm",
     "~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])@@@",
       "@@@STEP_LOG_LINE@python.inline@if not os.path.isdir(path):@@@",
       "@@@STEP_LOG_LINE@python.inline@  if os.path.exists(path):@@@",
@@ skipping 214 matching lines @@
       "SKIA_ANDROID_VERBOSE_SETUP": "1",
       "SKIA_OUT": "[SLAVE_BUILD]/out"
     },
     "name": "dm"
   },
   {
     "cmd": [
       "[SLAVE_BUILD]/skia/platform_tools/android/bin/adb_pull_if_needed",
       "--verbose",
       "/storage/emulated/legacy/skiabot/skia_dm",
-      "[SWARM_OUT_DIR]/dm"
+      "[CUSTOM_[SWARM_OUT_DIR]]/dm"
     ],
     "env": {
       "ANDROID_HOME": "/b/android-sdk-linux",
       "ANDROID_SDK_ROOT": "/b/android-sdk-linux",
       "BUILDTYPE": "Release",
       "CHROME_HEADLESS": "1",
       "GYP_DEFINES": "skia_arch_type=arm skia_warnings_as_errors=0",
       "PATH": "[DEPOT_TOOLS]:%(PATH)s",
       "PYTHONPATH": "[BUILD]/scripts",
       "SKIA_ANDROID_VERBOSE_SETUP": "1",
@@ skipping 96 matching lines @@
       "SKIA_OUT": "[SLAVE_BUILD]/out"
     },
     "name": "kill-server"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]