Modify Skia recipes to allow running XSAN on Swarming.

scripts/slave/recipes/skia/swarm_test.expected/Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Debug.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]/skia/tools/buildbot_spec.py",
       "/path/to/tmp/json",
       "Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Debug"
     ],
     "cwd": "[SLAVE_BUILD]/skia",
@@ skipping 51 matching lines @@
       "[SLAVE_BUILD]/tmp/SK_IMAGE_VERSION",
       "/path/to/tmp/"
     ],
     "name": "Get downloaded SK_IMAGE_VERSION"
   },
   {
     "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 108 matching lines @@
       "CPU",
       "cpu_or_gpu_value",
       "AVX2",
       "model",
       "GCE",
       "os",
       "Ubuntu",
       "--uninterestingHashesFile",
       "[SLAVE_BUILD]/tmp/uninteresting_hashes.txt",
       "--writePath",
-      "[SWARM_OUT_DIR]/dm",
+      "[CUSTOM_[SWARM_OUT_DIR]]/dm",
       "--nogpu",
       "--dummy-flags"
     ],
     "env": {
       "BUILDTYPE": "Debug",
       "CHROME_HEADLESS": "1",
       "GYP_DEFINES": "skia_arch_type=x86_64 skia_gpu=0 skia_warnings_as_errors=0",
       "PATH": "[DEPOT_TOOLS]:%(PATH)s",
       "PYTHONPATH": "[BUILD]/scripts",
       "SKIA_OUT": "[SLAVE_BUILD]/out"
     },
     "name": "dm"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]