Fix RenderedDocumentMarker::nullifyRenderedRect.

There obviously had to be assignment.

Also I changed return types to be void since they're unused, and
simplified updateMarkerRenderedRect a bit.

Relevant CL: https://codereview.chromium.org/2034363002

R=keishi
BUG=

Review-Url: https://codereview.chromium.org/2125693003
Cr-Commit-Position: refs/heads/master@{#403868}
2 files changed