Revert 232056 "Move ExtensionSystem references out of ExtensionA..."

> Move ExtensionSystem references out of ExtensionAppModelBuilder.
> 
> BUG=310376
> 
> Review URL: https://codereview.chromium.org/52143002

TBR=koz@chromium.org

Review URL: https://codereview.chromium.org/49533004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232188 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232188
Removing extraneous pymod_do_main directory from gyp_chromium.

R=abarth@chromium.org, adamk@chromium.org
BUG=297477

Review URL: https://codereview.chromium.org/26853002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232189 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232189