Revert "Add a flag for enabling/disabling the new accelerated scrolling path"

This reverts commit 429530bcff087403123cecafedbd93022fb74746.

>    Add a flag for enabling/disabling the new accelerated scrolling path
>
>    We now have two accelerated scrolling paths. One accelerates scrolling whenever
>    it's safe to promote the overflow scrolling div to a stacking container /
>    containing block and not break stacking or clipping.
>
>    The new path, the 'universal' path, enables accelerated scrolling in those cases
>    where the old path would not opt-in.
>
>    Eventually, we'd like to eliminate the old path, but this will require layer
>    squashing (the new path can result in many composited layers that ought to be
>    combined -- i.e., a 'layer explosion'). Until these paths are mature, we need to
>    be able to enable and disable them both, so we have two separate sets of flags.
>
>    Once we've eliminated the old path, we can replace both with
>    --[enable/disable]-accelerated-overflow-scroll (and eventually get rid of both
>    sets of flags).
>
>    BUG=None
>
>    Review URL: https://codereview.chromium.org/26809004

TBR=jamser@chromium.org
BUG=307486

Review URL: https://codereview.chromium.org/27393002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228743 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228743