Hook up GN to the GYP build system.

Hook up GN to the GYP build system.

This is a reland of 236542 and 238454 (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
TBR=bradnelson@google.com

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=238475

[brettw, 2013-12-03 23:14:53]

Committed patchset #2 manually as r238475 (presubmit successful).

[trchen, 2013-12-04 00:39:52]

This patch seems to cause many failures. I saw jam and thakis both submitted fix
for their use cases. Android's clang bot is still failing.

I have no idea what this thing does. Is it easy to fix it or revert it?

[Nico, 2013-12-04 00:41:14]

On 2013/12/04 00:39:52, trchen wrote:
> This patch seems to cause many failures. I saw jam and thakis both submitted
fix
> for their use cases. Android's clang bot is still failing.

link?

> 
> I have no idea what this thing does. Is it easy to fix it or revert it?