Drop Precise blink builders on chromium.webkit, add corresponding Trusty builders.

scripts/slave/recipes/chromium.expected/full_chromium_webkit_WebKit_Linux_Trusty.json

 [
   {
     "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",
       "[BUILDER_CACHE]/linux_layout",
       "511"
     ],
     "name": "makedirs checkout path",
@@ skipping 322 matching lines @@
       "--build-data-dir",
       "[ROOT]/build_data_dir",
       "--compiler",
       "goma",
       "--goma-jsonstatus",
       "/path/to/tmp/json",
       "--goma-service-account-json-file",
       "/creds/service_accounts/service-account-goma-client.json",
       "--goma-dir",
       "[CACHE]/cipd/goma",
+      "--ninja-ensure-up-to-date",
       "--",
       "blink_tests",
       "browser_tests",
       "browser_tests_run"
     ],
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "compile",
     "~followup_annotations": [
@@ skipping 171 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@sys.exit(1)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]