First pass at blink platform GN build that compiles.

There are still some TODO(GYP)s in there for specific platforms, and some dependencies aren't completed. I added a v8 stub config to set up the include dirs so this isn't blocked on the V8 build.

R=dpranke@chromium.org

Review URL: https://codereview.chromium.org/294073004

git-svn-id: svn://svn.chromium.org/blink/trunk@174466 bbb929c8-8fbe-4397-9dbb-9b2b20218538