Avoid markDirty when removing out-of-flow line boxes.

Previously, we did a markDirty(false) on the root line box in order to
rectify the dirtyness caused by removing out-of-flow line boxes after layout.
However, there were line boxes between root line box and the out-of-flow box
that were left dirty. Instead we now avoid calling markDirty in the first
place and remove the rectification code.

Likewise, avoid markDirty when removing empty text renderers as mentioned in
the removed comment. I tried to stop removing line boxes for the empty text
renderers as the FIXME says, but the changed test expectations got too scary.

Alternatively, we would have had to traverse the line box tree until we had
cleaned all dirty bits.

R=leviw@chromium.org,eseidel@chromium.org
BUG=362671

Review URL: https://codereview.chromium.org/254573006

git-svn-id: svn://svn.chromium.org/blink/trunk@172550 bbb929c8-8fbe-4397-9dbb-9b2b20218538