Need to take an element's scroll offset into account when painting its column rules.

R=
BUG=236315

Review URL: https://chromiumcodereview.appspot.com/14238038

git-svn-id: svn://svn.chromium.org/blink/trunk@158386 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Clip region based columns properly.

Need to call RenderRegion::overflowRectForFlowThreadPortion() first,
and THEN clip in the column gaps. overflowRectForFlowThreadPortion()
expands the logical left and right to the flow thread's overflow
rectangle, effectively defeating inline direction clipping completely.

This patch is ported from WebKit.
https://bugs.webkit.org/show_bug.cgi?id=118499
Reviewed in WebKit by David Hyatt.

BUG=269441

Review URL: https://chromiumcodereview.appspot.com/22577002

git-svn-id: svn://svn.chromium.org/blink/trunk@158387 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Use an std::set for keeping track of CSS order values.

Previously we would store the values in a Vector and sort it.
This will save memory by not needing to keep the Vector and it
is simpler.

BUG=None

Review URL: https://chromiumcodereview.appspot.com/24632003

git-svn-id: svn://svn.chromium.org/blink/trunk@158388 bbb929c8-8fbe-4397-9dbb-9b2b20218538