Add presubmit trybot for skia.

scripts/slave/recipes/run_presubmit.expected/skia.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "tryserver.chromium.linux",
       "--builder",
       "chromium_presubmit",
       "--slave",
       "TestSlavename",
       "--spec",
-      "cache_dir = '[ROOT]/git_cache'\nsolutions = [{'deps_file': '.DEPS.git', 'managed': True, 'name': 'build', 'url': 'https://chromium.googlesource.com/chromium/tools/build.git'}]",
+      "cache_dir = '[ROOT]/git_cache'\nsolutions = [{'deps_file': '.DEPS.git', 'managed': True, 'name': 'skia', 'url': 'https://skia.googlesource.com/skia.git'}]",
       "--root",
-      "build",
+      "skia",
       "--revision_mapping_file",
-      "{\"build\": \"got_revision\"}",
+      "{\"skia\": \"got_revision\"}",
       "--issue",
       "12853011",
       "--patchset",
       "1",
       "--rietveld_server",
       "https://codereview.chromium.org",
       "--output_json",
       "/path/to/tmp/json",
       "--revision",
-      "build@HEAD"
+      "skia@HEAD"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"did_run\": true, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"patch_failure\": false, @@@",
-      "@@@STEP_LOG_LINE@json.output@  \"patch_root\": \"build\", @@@",
+      "@@@STEP_LOG_LINE@json.output@  \"patch_root\": \"skia\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"properties\": {@@@",
-      "@@@STEP_LOG_LINE@json.output@    \"got_revision\": \"80754af91bfb6d1073585b046fe0a474ce868509\", @@@",
-      "@@@STEP_LOG_LINE@json.output@    \"got_revision_cp\": \"refs/heads/master@{#270553}\"@@@",
+      "@@@STEP_LOG_LINE@json.output@    \"got_revision\": \"9046e2e693bb92a76e972b694580e5d17ad10748\", @@@",
+      "@@@STEP_LOG_LINE@json.output@    \"got_revision_cp\": \"refs/heads/master@{#164710}\"@@@",
       "@@@STEP_LOG_LINE@json.output@  }, @@@",
-      "@@@STEP_LOG_LINE@json.output@  \"root\": \"build\", @@@",
+      "@@@STEP_LOG_LINE@json.output@  \"root\": \"skia\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"step_text\": \"Some step text\"@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@",
-      "@@@SET_BUILD_PROPERTY@got_revision@\"80754af91bfb6d1073585b046fe0a474ce868509\"@@@",
-      "@@@SET_BUILD_PROPERTY@got_revision_cp@\"refs/heads/master@{#270553}\"@@@"
+      "@@@SET_BUILD_PROPERTY@got_revision@\"9046e2e693bb92a76e972b694580e5d17ad10748\"@@@",
+      "@@@SET_BUILD_PROPERTY@got_revision_cp@\"refs/heads/master@{#164710}\"@@@"
     ]
   },
   {
     "cmd": [
       "git",
       "-c",
       "user.email=commit-bot@chromium.org",
       "-c",
       "user.name=The Commit Bot",
       "commit",
       "-a",
       "-m",
       "Committed patch"
     ],
-    "cwd": "[SLAVE_BUILD]/build",
+    "cwd": "[SLAVE_BUILD]/skia",
     "name": "commit git patch"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/presubmit_support.py",
       "--root",
-      "[SLAVE_BUILD]/build",
+      "[SLAVE_BUILD]/skia",
       "--commit",
       "--verbose",
       "--verbose",
       "--issue",
       "12853011",
       "--patchset",
       "1",
       "--skip_canned",
       "CheckRietveldTryJobExecution",
       "--skip_canned",
       "CheckTreeIsOpen",
       "--skip_canned",
       "CheckBuildbotPendingBuilds",
       "--rietveld_url",
       "https://codereview.chromium.org",
       "--rietveld_fetch",
       "--upstream",
-      "80754af91bfb6d1073585b046fe0a474ce868509",
+      "9046e2e693bb92a76e972b694580e5d17ad10748",
       "--trybot-json",
       "/path/to/tmp/json",
       "--rietveld_email",
       ""
     ],
     "cwd": "[SLAVE_BUILD]",
-    "env": {
-      "PYTHONPATH": ""
-    },
     "name": "presubmit",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@[@@@",
       "@@@STEP_LOG_LINE@json.output@  [@@@",
       "@@@STEP_LOG_LINE@json.output@    \"chromium_presubmit\", @@@",
       "@@@STEP_LOG_LINE@json.output@    [@@@",
       "@@@STEP_LOG_LINE@json.output@      \"compile\"@@@",
       "@@@STEP_LOG_LINE@json.output@    ]@@@",
       "@@@STEP_LOG_LINE@json.output@  ]@@@",
       "@@@STEP_LOG_LINE@json.output@]@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   }
 ]