Breakout while working on failing layout tests as part of  http://crbug.com/529938 .

To repro:

1. open fast/css/sticky/sticky-writing-mode-vertical-rl.html in content shell with --enable-blink-features=CSSStickyPosition
2. turn on paint flashing in dev console rendering settings
3. dev-tools inspect the rightmost div.sticky box
4. toggle background-color: green in the css .sticky class in dev tools to cause invalidation/repaint of the sticky boxes.
5. note that the rightmost box does not invalidate/repaint correctly.

From logging via showDebugData() in PaintController, it looks like the paint invalidation rect is missing application of the sticky offset. I can hack it by adding:

    if (isStickyPositioned())
        newBounds.setLocation(newLocation);

to LayoutObject.cpp:1434 but chrishtr@ notes this should likely be more properly done somewhere in the mapToVisualRectInAncestorSpace() and affiliated methods.

Leaving as P3 as this is an experimental feature.