Fix an assertion failure by Blink r150870.
Fix an assertion failure by Blink r150870.

CheckFocusedNodeTask is requested just after layout, however something
can set childNeedsStyleRecalc flag before CheckFocusedNodeTask is
executed.  CheckFocusedNodeTask should do nothing in such case, and
childNeedsStyleRecalc==true means we'll have layout soon.

Note that the assertion failure doesn't make user-visible problems.

BUG=247468
TEST=none; This issue depends on timing and it's hard to make a stable test.

Review URL: https://chromiumcodereview.appspot.com/16715004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@152111 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