Optimize check_gn_headers.py for speed

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

[wychen, 2017-04-24 23:35:29]

Description was changed from

==========
Optimize check_gn_headers.py for speed

Process the output of 'ninja' live through the pipe rather than waiting
for it to finish.

BUG=
==========

to

==========
Optimize check_gn_headers.py for speed

Process the output of 'ninja' live through the pipe rather than waiting
for it to finish.

BUG=661774
==========

[wychen, 2017-04-25 00:09:57]

Description was changed from

==========
Optimize check_gn_headers.py for speed

Process the output of 'ninja' live through the pipe rather than waiting
for it to finish.

BUG=661774
==========

to

==========
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
==========

[wychen, 2017-04-25 00:10:16]

wychen@chromium.org changed reviewers:
+ dpranke@chromium.org

[wychen, 2017-04-25 00:10:16]

PTAL

[Dirk Pranke, 2017-04-25 00:34:09]

lgtm

[wychen, 2017-04-25 06:18:00]

The CQ bit was checked by wychen@chromium.org

[commit-bot: I haz the power, 2017-04-25 06:18:21]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-04-25 06:30:18]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1493101080478750, "parent_rev":
"77c5ade43bf1d07f035d143ee6f3449d92b5d6ac", "commit_rev":
"6b609383cf3669b0670b567249ff868ea4b26e43"}

[commit-bot: I haz the power, 2017-04-25 06:30:28]

Description was changed from

==========
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
==========

to

==========
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/+/6b609383cf3669b0670b567249ff...
==========

[commit-bot: I haz the power, 2017-04-25 06:30:29]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/6b609383cf3669b0670b567249ff...

[wychen, 2017-04-26 04:09:00]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/2844623002/ by wychen@chromium.org.

The reason for reverting is: This optimization was buggy and broke the ninja
parsing..