Fix incorrect layout rects with 3d transforms.

Addresses https://code.google.com/p/trace-viewer/issues/detail?id=514

BUG=

Review URL: https://codereview.chromium.org/134973004

git-svn-id: svn://svn.chromium.org/blink/trunk@166544 bbb929c8-8fbe-4397-9dbb-9b2b20218538