Revert of Wrap buttons when necessary on chrome:extensions page. (patchset #1 id...

Revert of Wrap buttons when necessary on chrome:extensions page. (patchset #1 id:1 of https://codereview.chromium.org/719503002/)

Reason for revert:
It causes regression in http://crbug.com/432880.

Original issue's description:
> Wrap buttons when necessary on chrome:extensions page.
>
> - Put three buttons on the left into a div so that they can be wrapped;
> - Update "#devtools" to use display:flex;
> - Remove hard coded height for devtools element and use max-height for
>   css transition so that height is properly calculated with wrapping
>   while maintaining the css transition;
>
> BUG=321805
>
> Committed: https://crrev.com/ed3a098057b959014b0662a9fa410838f6ebcf4c
> Cr-Commit-Position: refs/heads/master@{#303766}

TBR=dbeam@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=321805

Review URL: https://codereview.chromium.org/726543004

Cr-Commit-Position: refs/heads/master@{#304285}