Change post-layout !needsLayout assert to ASSERT_WITH_SECURITY_IMPL

Hitting this assertion has security implications and should be marked
as such. Unfortunately, for performance reasons we cannot do this
for release builds.

BUG=282925

Review URL: https://chromiumcodereview.appspot.com/23819017

git-svn-id: svn://svn.chromium.org/blink/trunk@157153 bbb929c8-8fbe-4397-9dbb-9b2b20218538