[LayoutNG] Let NeedsTrailingSpaces() to fail if dirty tree

This patch let |NeedsTrailingSpaces()| work around reading
dirty tree, by assuming the trailing space is not collapsed.

Bug: 976203, 946004
Change-Id: Iae191c48d055f6b37d03d762db02888bc2c4026d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1666691
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670364}
1 file changed