chromium: Split up source into multiple outputs.

This splits up the source into one base output (just the build and tools
directory), one for bundled dependencies, one for sandbox sources and
one for the sources of the main browser.

The state of this is heavily work in progress and contains a bunch of
workarounds. For example, we currently copy the entire sources into the
build directory, so a build ultimately requires even more space than
before.

Of course, it's just temporary as neither GYP nor ninja is particularly
friendly if it comes to out-of-tree builds.

Another thing which is heavily WIP is how we handle patches. Ultimately,
those patches shouldn't be applied to the source tree (at least not all)
but rather to the final build's temporary directory.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>