Move GYP_DEFINES parsing to Python for GN

Hook up GN to the GYP build system.

This is a reland of 236542 (runs GN in GYP mode before actually running GYP), plus some additions

Move GYP_DEFINES parsing to Python for GN.

I pass in a GN-compatible list of variable sets on the command line from Python. This allows us to parse chromium.gyp_env and src/*/supplemental.gypi in Python like normal without having to duplicate Python dictionary parsing in GN.

Currently, GN does not produce any files used by the build, these will be added in a second step.

BUG=321352
R=bradnelson@google.com

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=238454

[brettw, 2013-11-19 00:29:36]

Note: depends on https://codereview.chromium.org/62803003/ landing first.

[bradn, 2013-11-19 17:45:57]

LGTM

Please add a bug number (you've got some bug tracking gn yes?)

https://codereview.chromium.org/73623005/diff/20003/build/gyp_chromium
File build/gyp_chromium (right):

https://codereview.chromium.org/73623005/diff/20003/build/gyp_chromium#newcode58
build/gyp_chromium:58: """Returns a list of the supplemental files that are
included in all GYP
FWIW These are usually meant to fix on one line.

[brettw, 2013-12-03 21:08:14]

Committed patchset #7 manually as r238454 (presubmit successful).

[Nico, 2013-12-03 22:45:15]

https://codereview.chromium.org/73623005/diff/170001/build/gyp_chromium
File build/gyp_chromium (right):

https://codereview.chromium.org/73623005/diff/170001/build/gyp_chromium#newco...
build/gyp_chromium:136: if subprocess.check_output(["file",
"/sbin/init"]).find("ELF 64-bit") >= 0:
(I think the usual thing to do is `getconf LONG_BIT`, fwiw)