Reland of Add helpful error messages to check_gn_headers.py

Reland of Add helpful error messages to check_gn_headers.py (patchset #1 id:1 of https://codereview.chromium.org/2905863002/ )

Reason for revert:
The real culprit is https://crrev.com/2903733004/, which was reverted.
This CL (https://crrev.com/2891363004) made it fail more gracefully, and should be kept.

Original issue's description:
> Revert of Add helpful error messages to check_gn_headers.py (patchset #3 id:40001 of https://codereview.chromium.org/2891363004/ )
> 
> Reason for revert:
> This CL is likely causing massive failures:
> 
> https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder/builds/84473
> to
> https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder/builds/84498
> 
> and 
> 
> https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder%20%28dbg%29/builds/111528
> to
> https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder%20%28dbg%29/builds/111542
> 
> Original issue's description:
> > Add helpful error messages to check_gn_headers.py
> > 
> > Before running check_gn_headers.py, it is necessary to build all
> > in order to get the dependency info from the compiler. Directly
> > checking whether rebuilding is needed by running a build dry run
> > takes too long, so some heuristics are used instead.
> > 
> > BUG=661774
> > 
> > Review-Url: https://codereview.chromium.org/2891363004
> > Cr-Commit-Position: refs/heads/master@{#474588}
> > Committed: https://chromium.googlesource.com/chromium/src/+/0ceaba5ef538ce1780578d5e948641bc27f5829b
> 
> TBR=dpranke@chromium.org,tfarina@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
> 
> Review-Url: https://codereview.chromium.org/2905863002
> Cr-Commit-Position: refs/heads/master@{#474649}
> Committed: https://chromium.googlesource.com/chromium/src/+/d3c2681426db53550547f2bc115c3f72ba40f276

TBR=dpranke@chromium.org,tfarina@chromium.org,mahmadi@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/2907683002
Cr-Commit-Position: refs/heads/master@{#474786}
Committed: https://chromium.googlesource.com/chromium/src/+/0362911661559a7edca7d4ca9c36f1091a527b04

[wychen, 2017-05-25 20:36:01]

The CQ bit was checked by wychen@chromium.org

[wychen, 2017-05-25 20:36:01]

Created Reland of Add helpful error messages to check_gn_headers.py

[commit-bot: I haz the power, 2017-05-25 20:36:49]

CQ is trying da patch.

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

[Dirk Pranke, 2017-05-25 20:37:10]

lgtm

[commit-bot: I haz the power, 2017-05-25 20:37:21]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1495744561120930, "parent_rev":
"205bf376ac96ed889732bf1172883263213ea0fe", "commit_rev":
"39a08ca627f74fa042013463cb3f77e2a6ae2901"}

[commit-bot: I haz the power, 2017-05-25 20:37:46]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1495744561120930, "parent_rev":
"96ce0d19bedf3ed68b0ba5d342f22ada734dd26f", "commit_rev":
"0362911661559a7edca7d4ca9c36f1091a527b04"}

[commit-bot: I haz the power, 2017-05-25 20:38:22]

Description was changed from

==========
Reland of Add helpful error messages to check_gn_headers.py (patchset #1 id:1 of
https://codereview.chromium.org/2905863002/ )

Reason for revert:
The real culprit is https://crrev.com/2903733004/, which was reverted.
This CL (https://crrev.com/2891363004) made it fail more gracefully, and should
be kept.

Original issue's description:
> Revert of Add helpful error messages to check_gn_headers.py (patchset #3
id:40001 of https://codereview.chromium.org/2891363004/ )
> 
> Reason for revert:
> This CL is likely causing massive failures:
> 
>
https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder/builds/8...
> to
>
https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder/builds/8...
> 
> and 
> 
>
https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder%20%28dbg...
> to
>
https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder%20%28dbg...
> 
> Original issue's description:
> > Add helpful error messages to check_gn_headers.py
> > 
> > Before running check_gn_headers.py, it is necessary to build all
> > in order to get the dependency info from the compiler. Directly
> > checking whether rebuilding is needed by running a build dry run
> > takes too long, so some heuristics are used instead.
> > 
> > BUG=661774
> > 
> > Review-Url: https://codereview.chromium.org/2891363004
> > Cr-Commit-Position: refs/heads/master@{#474588}
> > Committed:
https://chromium.googlesource.com/chromium/src/+/0ceaba5ef538ce1780578d5e9486...
> 
> TBR=dpranke@chromium.org,tfarina@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
> 
> Review-Url: https://codereview.chromium.org/2905863002
> Cr-Commit-Position: refs/heads/master@{#474649}
> Committed:
https://chromium.googlesource.com/chromium/src/+/d3c2681426db53550547f2bc115c...

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

to

==========
Reland of Add helpful error messages to check_gn_headers.py (patchset #1 id:1 of
https://codereview.chromium.org/2905863002/ )

Reason for revert:
The real culprit is https://crrev.com/2903733004/, which was reverted.
This CL (https://crrev.com/2891363004) made it fail more gracefully, and should
be kept.

Original issue's description:
> Revert of Add helpful error messages to check_gn_headers.py (patchset #3
id:40001 of https://codereview.chromium.org/2891363004/ )
> 
> Reason for revert:
> This CL is likely causing massive failures:
> 
>
https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder/builds/8...
> to
>
https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder/builds/8...
> 
> and 
> 
>
https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder%20%28dbg...
> to
>
https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder%20%28dbg...
> 
> Original issue's description:
> > Add helpful error messages to check_gn_headers.py
> > 
> > Before running check_gn_headers.py, it is necessary to build all
> > in order to get the dependency info from the compiler. Directly
> > checking whether rebuilding is needed by running a build dry run
> > takes too long, so some heuristics are used instead.
> > 
> > BUG=661774
> > 
> > Review-Url: https://codereview.chromium.org/2891363004
> > Cr-Commit-Position: refs/heads/master@{#474588}
> > Committed:
https://chromium.googlesource.com/chromium/src/+/0ceaba5ef538ce1780578d5e9486...
> 
> TBR=dpranke@chromium.org,tfarina@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
> 
> Review-Url: https://codereview.chromium.org/2905863002
> Cr-Commit-Position: refs/heads/master@{#474649}
> Committed:
https://chromium.googlesource.com/chromium/src/+/d3c2681426db53550547f2bc115c...

TBR=dpranke@chromium.org,tfarina@chromium.org,mahmadi@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/2907683002
Cr-Commit-Position: refs/heads/master@{#474786}
Committed:
https://chromium.googlesource.com/chromium/src/+/0362911661559a7edca7d4ca9c36...
==========

[commit-bot: I haz the power, 2017-05-25 20:38:23]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/0362911661559a7edca7d4ca9c36...