Verify FormatType in ScopedClipboardWriter::WritePickledData.

BUG=352395
R=tony@chromium.org
TBR=sky@chromium.org

Review URL: https://codereview.chromium.org/199763002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256974 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256974