Adjust source paths so we don't need to use rebase_path() on all of them.

BUG=angleproject:1569

Change-Id: I687dbb9378b1f054eb5664320c662fe4c882a82f
Reviewed-on: https://chromium-review.googlesource.com/1194619
Commit-Queue: Frank Henigman <fjhenigman@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>