editing/pasteboard/paste-noscript.html ASSERTs in force composting mode

This CL adds a new legal transition in the DocumentLifecycle state machine to
let us synchronously recalc style in a post layout task. Conceptually, that
doesn't make a whole lot of sense because nothing in layout should dirty style
information, but that appears to happen in this test.

We can work to remove this transition from the state machine in the future.

R=ojan@chromium.org
BUG=363844

Review URL: https://codereview.chromium.org/242423005

git-svn-id: svn://svn.chromium.org/blink/trunk@171991 bbb929c8-8fbe-4397-9dbb-9b2b20218538