Revert 233875 "[Files.app] Make the file-type dropbox at the bot..."

> [Files.app] Make the file-type dropbox at the bottom hidden by default.
> 
> Sometimes, it could be seen during initialization. 
> 
> BUG=316133
> TEST=manually tested
> 
> Review URL: https://codereview.chromium.org/61733007

TBR=yoshiki@chromium.org

Review URL: https://codereview.chromium.org/68733004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234279 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234279