Add forgive_all to enable experimental builders.

scripts/slave/gatekeeper.json

 {
   "comment": ["This is a configuration file for gatekeeper_ng.py",
               "Look at that for documentation on this file's format."],
 
   "masters": {
     "http://build.chromium.org/p/chromium": [
       {
         "categories": [
           "gclient"
         ],
 
-        "sheriff_classes": [
-          "sheriff"
-        ],
+        "forgive_all": "true",
 
         "builders": {
           "Win": {
             "categories": [
               "chromium_archive_build",
               "chromium_checkdeps2git",
               "chromium_compile",
               "chromium_crash_handler",
               "chromium_sizes",
               "chromium_windows"
@@ skipping 33 matching lines @@
           "Android": {
             "comment": ["Android slave_steps aren't enabled in",
                         "master_full_cfg.py."]
           }
         }
       }
     ],
     "http://build.chromium.org/p/chromium.lkgr": [
       {
         "tree_notify": [
-          "jschuh@chromium.org"
+          "jschuh@chromium.org",
+          "scottmg@chromium.org",
+          "wfh@chromium.org"
         ],
 
+        "forgive_all": "true",
+
         "builders": {
           "Win x64": {
             "categories": [
               "chromium_archive_build",
               "chromium_compile",
               "chromium_windows",
               "gclient"
             ]
           }
         }
@@ skipping 44 matching lines @@
       ]
     },
 
     "chromium_archive_build": {
       "forgiving_steps": [
         "archive_build"
       ]
     }
   }
 }