Improve mitigation from r109406 to reset layout root in cases when document is getting destroyed.
Improve mitigation from r109406 to reset layout root in cases when document is getting destroyed.

BUG=209604
TEST=No test since it is flaky and will be tracked in a seperate functional bug to analyze why RenderSVGRoot is left as a layout root. Fix tested under ASAN.
R=schenney@chromium.org

Review URL: https://codereview.chromium.org/14846011

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@149745 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs