Don't pixel snap for ellipsis

This is a rough port of Zalan Bujtas' patch on https://bugs.webkit.org/show_bug.cgi?id=112227

Due to pixel snapping/truncating, we prematurely truncate some rtl content when
text-overflow: ellipsis is enabled. One piece of this puzzle is a hack to fix old
multi-column code, which didn't work well with sub-pixel layout. The other
is unnecessary pixel snapping in ellipsis line layout. Both of these issues need to
be fixed to address the bug in rtl ellipsis content.

This changes old-multicolumn layout by one pixel when compared to the (better)
region-based multicolumn on 2 ref tests.

BUG=378489

Review URL: https://codereview.chromium.org/303673007

git-svn-id: svn://svn.chromium.org/blink/trunk@175434 bbb929c8-8fbe-4397-9dbb-9b2b20218538