Revert 238454 "Hook up GN to the GYP build system."

Revert 238454 "Hook up GN to the GYP build system."

> 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
> 
> Review URL: https://codereview.chromium.org/73623005

TBR=brettw@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=238459

[brettw, 2013-12-03 21:21:16]

Committed patchset #1 manually as r238459.