updateDescendantDependentFlags before updating compositing

This CL changes makes the compositing update call updateDescendantDependentFlags
before entering InCompositingUpdate because updateDescendantDependentFlags can
generate dirtiness that the compositing update needs to clean.

Also, remove a number of unnecessary calls to updateDescendantDependentFlags and
one unnecessary call to updateZOrderLists.  Now that these functions are called
only during the compositing update, we know that this information is already
up-to-date.

Review URL: https://codereview.chromium.org/340343004

git-svn-id: svn://svn.chromium.org/blink/trunk@176637 bbb929c8-8fbe-4397-9dbb-9b2b20218538