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
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=238253
Review URL: https://codereview.chromium.org/
68133020
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238531 0039d316-1c4b-4281-b951-d872f2087c98