Move clipboard-related webkit_glue embedder functions into a ClipboardClient interface.

      This moves the functions into a pattern that is component-friendly.

BUG=98755
TEST=Chrome, DRT, test_shell

Review URL: http://codereview.chromium.org/8591030

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@111097 0039d316-1c4b-4281-b951-d872f2087c98