gn: Tweak precompiled_header docs.

gn: Tweak precompiled_header docs.

Add an entry for precompiled_header_type, and document
GCC-style precompiled headers a bit.

BUG=none

Review-Url: https://codereview.chromium.org/2734523002
Cr-Commit-Position: refs/heads/master@{#454685}
Committed: https://chromium.googlesource.com/chromium/src/+/698727682cc73ad3770d402395d23096f572d3f2

[Nico, 2017-03-03 20:22:46]

The CQ bit was checked by thakis@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-03-03 20:23:07]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Nico, 2017-03-03 20:24:33]

thakis@chromium.org changed reviewers:
+ brettw@chromium.org

[Nico, 2017-03-03 20:24:34]

https://codereview.chromium.org/2734523002/diff/1/tools/gn/variables.cc
File tools/gn/variables.cc (right):

https://codereview.chromium.org/2734523002/diff/1/tools/gn/variables.cc#newco...
tools/gn/variables.cc:1471: headers.
Fairly inconsistent with how MSVC-stype PCH works in GN, but that's today's
behavior from what I can tell. Chromium's .gn files do set precompiled_header
for GCC-style PCHs, but from what I can tell it has no effect. (Maybe GN should
warn if precompiled_header is set for gcc-style PCHs?)

https://codereview.chromium.org/2734523002/diff/1/tools/gn/variables.cc#newco...
tools/gn/variables.cc:1478: an #include line in source code. The compiler will
match this string against
The motivation behind this CL was that the #include at the start of the line got
formatted as a comment in `gn help` output.

[commit-bot: I haz the power, 2017-03-03 20:34:57]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-03-03 20:34:57]

Dry run: This issue passed the CQ dry run.

[Dirk Pranke, 2017-03-03 21:39:36]

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

[Dirk Pranke, 2017-03-03 21:39:37]

lgtm

[Nico, 2017-03-03 21:41:32]

The CQ bit was checked by thakis@chromium.org

[commit-bot: I haz the power, 2017-03-03 21:41:44]

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, 2017-03-03 21:45:37]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1488577292750000, "parent_rev":
"291cbdce8960e700e68675fc32258dec3095ae82", "commit_rev":
"698727682cc73ad3770d402395d23096f572d3f2"}

[commit-bot: I haz the power, 2017-03-03 21:46:19]

Description was changed from

==========
gn: Tweak precompiled_header docs.

Add an entry for precompiled_header_type, and document
GCC-style precompiled headers a bit.

BUG=none
==========

to

==========
gn: Tweak precompiled_header docs.

Add an entry for precompiled_header_type, and document
GCC-style precompiled headers a bit.

BUG=none

Review-Url: https://codereview.chromium.org/2734523002
Cr-Commit-Position: refs/heads/master@{#454685}
Committed:
https://chromium.googlesource.com/chromium/src/+/698727682cc73ad3770d402395d2...
==========

[commit-bot: I haz the power, 2017-03-03 21:46:21]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/698727682cc73ad3770d402395d2...