Revert 238253 "Fix dragging supported files to tab strip."

Probably due to submit order conflict this seems to have broken
Linux chromeos build (compile):
http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Builder/builds/60931

> Fix dragging supported files to tab strip.
> 
> Use the inferred MIME type of download items, rather than the server value,
> when deciding if the tab strip can allow a drop. Get the MIME type
> asynchronously so we don't crash (IO must be allowed in the call to
> GetMimeTypeFromFile).
> 
> Also check the profile's plugins when determining whether a MIME type is
> supported.
> 
> Regardless of whether a file is supported, the dragging operation should
> still be allowed so that spring-loaded tabs work with file drags.
> 
> BUG=274288
> R=asanka@chromium.org, sky@chromium.org
> 
> Review URL: https://codereview.chromium.org/68133020

TBR=michaelpg@chromium.org

Review URL: https://codereview.chromium.org/100773002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238260 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238260