Add layout states to DocumentLifecycle state machine

This CL adds a number of layout-related states to the DocumentLifecycle state
machine. Currently, we're using these states to ASSERT that we're making valid
transitions. Eventually, we'll switch over to these states as the source of
truth.

R=ojan@chromium.org
BUG=341627

Review URL: https://codereview.chromium.org/146023008

git-svn-id: svn://svn.chromium.org/blink/trunk@166765 bbb929c8-8fbe-4397-9dbb-9b2b20218538