[FastTextAutosizer] Fix the inline overlap issue.

Inline renderers have preferred logical widths that end up depending on
the autosizing font scale. This patch forces these preferred widths to
be recomputed. This recomputation is not necessary for text in blocks
because the block layout algorithm does not depend on the text width.
The parent null check (renderer->parent()...) is for list markers
which, interestingly, can not be in the render tree.

This patch fixes rendering on many sites, including hacker news.

BUG=338494

Review URL: https://codereview.chromium.org/218863002

git-svn-id: svn://svn.chromium.org/blink/trunk@170638 bbb929c8-8fbe-4397-9dbb-9b2b20218538