GN: Allow users to enable DCHECK on Release builds.

GN: Allow users to enable DCHECK on Release builds.

This declares dcheck_always_on argument (false by default) so users can
override it. If set to true this will make a compiler define
(DCHECK_ALWAYS_ON=1). This mirrors GYP counterpart.

Debug:

$ gn gen out_gn/Debug --args='dcheck_always_on=true'
$ ninja -v -C out_gn/Debug base

Release:

$ gn gen --args='is_debug=false dcheck_always_on=true' out_gn/Release
$ ninja -v -C out_gn/Release base

Manually checked that -DDCHECK_ALWAYS_ON=1 is passed on the command line
to the compiler.

BUG=None
TEST=see above
R=brettw@chromium.org

Committed: https://crrev.com/a52158d7c0b0c697d1625680fbaf9c2902d26da7
Cr-Commit-Position: refs/heads/master@{#314867}

[Mostyn Bramley-Moore, 2015-02-05 16:54:34]

mostynb@opera.com changed reviewers:
+ mostynb@opera.com

[Mostyn Bramley-Moore, 2015-02-05 16:54:35]

https://codereview.chromium.org/896413003/diff/1/build/config/BUILD.gn
File build/config/BUILD.gn (right):

https://codereview.chromium.org/896413003/diff/1/build/config/BUILD.gn#newcode23
build/config/BUILD.gn:23: # Set to true to enable dcheck in release.
nitpick: "in release builds." would be slightly more readable

[tfarina, 2015-02-05 17:05:19]

https://codereview.chromium.org/896413003/diff/1/build/config/BUILD.gn
File build/config/BUILD.gn (right):

https://codereview.chromium.org/896413003/diff/1/build/config/BUILD.gn#newcode23
build/config/BUILD.gn:23: # Set to true to enable dcheck in release.
On 2015/02/05 16:54:35, Mostyn Bramley-Moore wrote:
> nitpick: "in release builds." would be slightly more readable

Done. Also for common.gypi

[Dirk Pranke, 2015-02-05 17:08:11]

lgtm, but I think Brett wants to review any changes to the toplevel files in
//build ... (I expect this one will be fine).

[brettw, 2015-02-05 19:28:09]

lgtm

[tfarina, 2015-02-05 20:20:00]

tfarina@chromium.org changed reviewers:
+ scottmg@chromium.org

[tfarina, 2015-02-05 20:20:00]

Scott, could you approve this as build/OWNERS?

[Nico, 2015-02-05 20:31:51]

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

[Nico, 2015-02-05 20:31:52]

build lgtm

[Nico, 2015-02-05 20:31:56]

The CQ bit was checked by thakis@chromium.org

[commit-bot: I haz the power, 2015-02-05 20:32:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/896413003/20001

[commit-bot: I haz the power, 2015-02-05 20:36:25]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-05 20:37:12]

Patchset 2 (id:??) landed as
https://crrev.com/a52158d7c0b0c697d1625680fbaf9c2902d26da7
Cr-Commit-Position: refs/heads/master@{#314867}