Add runhooks step to AOSP bot to pick up essential build dependencies (like gn).

scripts/slave/recipes/android_webview_aosp.expected/does_delete_stale_chromium.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': '', 'managed': True, 'name': 'src', 'url': 'svn://svn-mirror.golo.chromium.org/chrome/trunk/src'}]"
     ],
@@ skipping 146 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": [
+      "python",
+      "-u",
+      "[DEPOT_TOOLS]/gclient.py",
+      "runhooks"
+    ],
+    "env": {
+      "GYP_CHROMIUM_NO_ACTION": "1"
+    },
+    "name": "gclient runhooks"
+  },
+  {
+    "cmd": [
       "[SLAVE_BUILD]/src/build/util/lastchange.py",
       "-o",
       "[SLAVE_BUILD]/src/build/util/LASTCHANGE",
       "-s",
       "[SLAVE_BUILD]/src"
     ],
     "name": "Chromium LASTCHANGE",
     "seed_steps": [
       "Chromium LASTCHANGE",
       "Blink LASTCHANGE"
@@ skipping 141 matching lines @@
       "--src-dir",
       "[SLAVE_BUILD]/android-src",
       "--build-tool",
       "make-android",
       "--verbose"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "compile"
   }
 ]