Add GCAPI to the GN build.

Add GCAPI to the GN build.

GCAPI is a Windows-specific API for distributors of Chrome.

This adds all chrome/installer targets to "gn check" and fixes many associated issues. The result codes targets are also added to "gn check" to make sure people don't accidentally add stuff to those headers.

Rather than add a disable for the size_t to int warning for this target, I just fixed the warning and removed the disable flag from GYP.

Merged //chrome/common:result_codes into //chrome/common:constants. This is basically a constant and everybody that needed the result codes already depended on the constants target.

Fix google_update build file. The midl template already did everything this file was trying to do. I clarified the template documentation a bit.

BUG=539428
Committed: https://crrev.com/f986f9572c792346194055784b9237820ffce52b
Cr-Commit-Position: refs/heads/master@{#352869}

[brettw, 2015-10-06 22:36:58]

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

[brettw, 2015-10-06 22:37:02]

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

[commit-bot: I haz the power, 2015-10-06 22:38:51]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1388943004/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1388943004/20001

[brettw, 2015-10-06 22:47:29]

Patchset #3 (id:40001) has been deleted

[Dirk Pranke, 2015-10-06 23:59:16]

lgtm

[brettw, 2015-10-07 17:04:12]

The CQ bit was checked by brettw@chromium.org

[commit-bot: I haz the power, 2015-10-07 17:05:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1388943004/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1388943004/20001

[commit-bot: I haz the power, 2015-10-07 17:18:23]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-07 17:23:10]

Patchset 2 (id:??) landed as
https://crrev.com/f986f9572c792346194055784b9237820ffce52b
Cr-Commit-Position: refs/heads/master@{#352869}