Add GN (the build tool) to the chromium.linux buildbots and try jobs

scripts/slave/recipes/chromium_gn.expected/unittest_basic.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "config",
       "--spec",
       "cache_dir = None\nsolutions = [{'custom_vars': {'googlecode_url': 'svn://svn-mirror.golo.chromium.org/%s', 'nacl_trunk': 'svn://svn-mirror.golo.chromium.org/native_client/trunk', 'sourceforge_url': 'svn://svn-mirror.golo.chromium.org/%(repo)s', 'webkit_trunk': 'svn://svn-mirror.golo.chromium.org/blink/trunk'}, 'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'url': 'svn://svn-mirror.golo.chromium.org/chrome/trunk/src'}]"
     ],
     "name": "gclient setup"
   },
   {
     "abort_on_failure": true,
     "cmd": [
       "python",
       "-u",
+      "[BUILD]/scripts/slave/gclient_safe_revert.py",
+      ".",
+      "[DEPOT_TOOLS]/gclient"
+    ],
+    "name": "gclient revert"
+  },
+  {
+    "abort_on_failure": true,
+    "cmd": [
+      "python",
+      "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "sync",
       "--nohooks",
       "--delete_unversioned_trees",
       "--force",
       "--output-json",
       "/path/to/tmp/json"
     ],
     "name": "gclient sync",
     "~followup_annotations": [
@@ skipping 23 matching lines @@
       "@@@SET_BUILD_PROPERTY@got_nacl_revision@274981@@@",
       "@@@SET_BUILD_PROPERTY@got_webkit_revision@124383@@@",
       "@@@SET_BUILD_PROPERTY@got_swarming_client_revision@276089@@@",
       "@@@SET_BUILD_PROPERTY@got_webrtc_revision@120644@@@",
       "@@@SET_BUILD_PROPERTY@got_revision@170242@@@",
       "@@@SET_BUILD_PROPERTY@got_swarm_client_revision@200767@@@"
     ]
   },
   {
     "cmd": [
-      "[SLAVE_BUILD]/src/tools/telemetry/build/generate_telemetry_harness.sh",
-      "[TMP_BASE]/telemetry-harness_tmp_1/telemetry-170242.zip"
-    ],
-    "name": "create harness archive"
-  },
-  {
-    "cmd": [
       "python",
       "-u",
-      "[DEPOT_TOOLS]/third_party/gsutil/gsutil",
-      "cp",
-      "[TMP_BASE]/telemetry-harness_tmp_1/telemetry-170242.zip",
-      "gs://chromium-telemetry/snapshots/telemetry-170242.zip"
+      "[DEPOT_TOOLS]/gclient.py",
+      "runhooks"
     ],
-    "name": "gsutil upload",
-    "~followup_annotations": [
-      "@@@STEP_LINK@gsutil.upload@https://storage.cloud.google.com/chromium-telemetry/snapshots/telemetry-170242.zip@@@"
-    ]
+    "env": {
+      "GYP_CHROMIUM_NO_ACTION": "1"
+    },
+    "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
-      "\nimport shutil, sys\nshutil.rmtree(sys.argv[1])\n",
-      "[TMP_BASE]/telemetry-harness_tmp_1"
+      "[DEPOT_TOOLS]/gn.py",
+      "--root=[SLAVE_BUILD]/src",
+      "gen",
+      "//out/Debug",
+      "--args=is_debug=true"
     ],
-    "name": "rmtree remove harness temp directory",
-    "~followup_annotations": [
-      "@@@STEP_LOG_LINE@python.inline@@@@",
-      "@@@STEP_LOG_LINE@python.inline@import shutil, sys@@@",
-      "@@@STEP_LOG_LINE@python.inline@shutil.rmtree(sys.argv[1])@@@",
-      "@@@STEP_LOG_END@python.inline@@@"
-    ]
+    "name": "gn"
+  },
+  {
+    "cmd": [
+      "[DEPOT_TOOLS]/ninja",
+      "-C",
+      "[SLAVE_BUILD]/src/out/Debug"
+    ],
+    "name": "compile"
   }
 ]