Revert 256930 "Add 9 patch scrollbar assets to native theme"

> Add 9 patch scrollbar assets to native theme
> 
> 9-patch scrollbar is a prettified version of overlay scrollbar that is
> going to be used on aura. Add these assets with their ID to native theme
>  aura. Add logic to use 9 patch scroll bar assets when overlay scrollbar
>  is enabled. Also overlay scrollbar should only be painting thumbs, thus
>  when overlay scrollbar is turned on native theme shouldn't need to
> paint track and scrollbar corner.
> 
> This set of assets for 9 patch scrollbar intent to control stroke and
> fill separately, while stroke does not provide asset for center of
> 9 patch. Different state is achieved by adjusting alpha of stroke and
> fill separately.
> 
> BUG=307578
> 
> Review URL: https://codereview.chromium.org/183973008

TBR=weiliangc@chromium.org

Review URL: https://codereview.chromium.org/198193006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256948 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256948