Fix (most) generated includes to have gen/ in their path.
This makes it easier to tell where files exist on disk.
Unfortunately I had to leave the old include path
in engine/BUILD.gn to support all the v8 includes
which were too many to deal with in this patch.
It's a little nasty to have the raw build directory
in our include path, but it produces nicer paths.
R=abarth@chromium.org
This just removes a random subset of vertical writing mode bits
that I grepped for. There's a ton more to do, but it seems best to
do it in chunks.
The key things for understanding this patch, isWritingModeRoot is
always false and isHorizontalWritingMode is always true. Also,
we're never flipped* modes of any kind, so we can undo any flipping.
R=esprehn@chromium.org
Review URL: https://codereview.chromium.org/688213002
