s/setNeedsLayout(false)/clearNeedsLayout().

It shares exactly 1 line of code with setNeedsLayout(true) and
is inconsistent with all the other setNeedsFooLayout methods.

Review URL: https://chromiumcodereview.appspot.com/22439011

git-svn-id: svn://svn.chromium.org/blink/trunk@155896 bbb929c8-8fbe-4397-9dbb-9b2b20218538