Avoid double layout for writing mode roots if LayoutNG is enabled

In legacy code we perform a series of subtree layouts that can be
avoided in LayoutNG code.

This patch disables layoutOrthogonalWritingModeRoots if layoutNG is
enabled.

BUG=635619

Review-Url: https://codereview.chromium.org/2666663002
Cr-Commit-Position: refs/heads/master@{#447083}
1 file changed