Oilpan: zap unused memory when running with LSan.

If we leave old pointer values in the heap when running with LSan they
will be treated as part of the root set for LSan which could hide real
leak.

R=haraken@chromium.org, tkent@chromium.org
BUG=378404

Review URL: https://codereview.chromium.org/309943003

git-svn-id: svn://svn.chromium.org/blink/trunk@175347 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove unused setNeedsStyleRecalc.

Since r175255 made StyleEngine CSSFontSelectorClient, we don't need
to think about whether we have StyleResolver or not.

BUG=369401
TEST=All tests should pass, just refactoring.

Review URL: https://codereview.chromium.org/312643002

git-svn-id: svn://svn.chromium.org/blink/trunk@175348 bbb929c8-8fbe-4397-9dbb-9b2b20218538