Do not force scrollbar update if parameters didn't change (reland).

This fixes a bug where scrollbar animations fire indefinitely, which
is a serious battery issue.  Relanding after fixing affected layout tests.

BUG=341145
NOTRY=true

Review URL: https://codereview.chromium.org/138013006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249855 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249855