Revert of Check missing headers in the build on CQ (patchset chromium#8…

… id:160001 of https://codereview.chromium.org/2628543003/ )

Reason for revert:
This CL likely breaks |check_gn_headers| step. See crbug.com/725877 for details.

Original issue's description:
> Check missing headers in the build on CQ
>
> This script is run on the following bots on CQ:
> - linux_chromium_dbg_ng
> - linux_chromium_rel_ng
>
> Note that this script can only be added to bots that have "all"
> in "additional_compile_targets".
>
> BUG=661774
>
> Review-Url: https://codereview.chromium.org/2628543003
> Cr-Commit-Position: refs/heads/master@{#474218}
> Committed: https://chromium.googlesource.com/chromium/src/+/ded5e27012a9b0d50de4b80a16e024fe5106b160

TBR=dpranke@chromium.org,thakis@chromium.org,wychen@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=661774,725877

Review-Url: https://codereview.chromium.org/2900143004
Cr-Commit-Position: refs/heads/master@{#474256}

build/check_gn_headers.py

@@ -163,14 +163,13 @@ def main():
   if args.whitelist:
     whitelist = ParseWhiteList(open(args.whitelist).read())
     missing -= whitelist
-    nonexisting -= whitelist
 
   missing = sorted(missing)
   nonexisting = sorted(nonexisting)
 
   if args.json:
     with open(args.json, 'w') as f:
-      json.dump(sorted(missing + nonexisting), f)
+      json.dump(missing, f)
 
   if len(missing) == 0 and len(nonexisting) == 0:
     return 0