Refactor ncClipboard::GetData() for better readability, add nsClipboard::SetTransferableData()
to send clipboard data to nsITransferable.
According to Gtk people [1] we can't mix free()/g_free() and malloc()/g_malloc() calls.
Existing nsClipboard code mixes that on some places which can lead to issued on glib built
with specific flags (ENABLE_MEM_PROFILE or ENABLE_MEM_CHECK).
[1] https://mail.gnome.org/archives/gtk-list/2000-July/msg00002.html
MozReview-Commit-ID: GvkUGSttVGO
--HG--
extra : rebase_source : 99801e1dc97e24a8d68fe7f3585562bb541c6628
