Make ClipboardHostMsg_WriteObjectsSync return more quickly.

BUG=none

Review URL: https://codereview.chromium.org/79153005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237040 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237040