Revert of Optimize check_gn_headers.py for speed (patchset #1 id:1 of https://codereview.chromium.org/2842513003/ )

Reason for revert:
This optimization was buggy and broke the ninja parsing.

Original issue's description:
> Optimize check_gn_headers.py for speed
>
> Process the output of 'ninja' live through the pipe rather than waiting
> for it to finish.
>
> Before:
> 20.74user 16.36system 0:24.57elapsed 151%CPU
>
> After:
> 16.63user 9.24system 0:13.94elapsed 185%CPU
>
> BUG=661774
>
> Review-Url: https://codereview.chromium.org/2842513003
> Cr-Commit-Position: refs/heads/master@{#466900}
> Committed: https://chromium.googlesource.com/chromium/src/+/6b609383cf3669b0670b567249ff868ea4b26e43

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

Review-Url: https://codereview.chromium.org/2844623002
Cr-Commit-Position: refs/heads/master@{#467231}


CrOS-Libchrome-Original-Commit: c219b8a1823f884703c3546bf2cb7c17fb737d67
2 files changed
tree: 3b56c4f344a0b8302896d837e8028c879698e9ae
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/