Make landmines handle GN build directories better.

Make landmines handle GN build directories better.

GN has user-managed build output directories, and the build arguments are saved in those directories. This means that when you hit a landmine, the user will be forced to regenerate that build directory, and to respecify their build arguments.

This change makes the landmine script look for GN build directories. If one is found, the build and command-line arguments to GN are preserved, and enough of a bootstrap build is left in that directory to regenerate itself the next time the build is run. This should make landmines transparent to GN users (except of course that everything will be rebuilt).

Committed: https://crrev.com/f5b2cda7e05f7ffa4ac57b6a00d9cd52c1e0ac87
Cr-Commit-Position: refs/heads/master@{#303528}

[brettw, 2014-11-10 19:20:28]

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

[Dirk Pranke, 2014-11-10 22:14:00]

lgtm w/ nit.

https://codereview.chromium.org/709813003/diff/1/build/landmines.py
File build/landmines.py (right):

https://codereview.chromium.org/709813003/diff/1/build/landmines.py#newcode85
build/landmines.py:85: shutil.rmtree(build_dir)
nit: I would early exit here.

[brettw, 2014-11-10 22:23:17]

The CQ bit was checked by brettw@chromium.org

[commit-bot: I haz the power, 2014-11-10 22:23:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/709813003/20001

[commit-bot: I haz the power, 2014-11-10 23:08:14]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-11-10 23:09:02]

Patchset 2 (id:??) landed as
https://crrev.com/f5b2cda7e05f7ffa4ac57b6a00d9cd52c1e0ac87
Cr-Commit-Position: refs/heads/master@{#303528}