Revert "Ensure that if FrameView::isScrollable() is false, the assoc WebLayer is, too."

This change reverts r164629; this is a speculative revert to see
if this change broke some Android unit tests. It looks like
this change also broke some layout tests. See comments on the bug
for more details.

TBR=vollick@chromium.org, adamk@chromium.org
BUG=328672

Review URL: https://codereview.chromium.org/127303003

git-svn-id: svn://svn.chromium.org/blink/trunk@164653 bbb929c8-8fbe-4397-9dbb-9b2b20218538