This patch does the following:
* It adds nsITransferable::Init(nsILoadContext*). The load context
might be null, which means that the transferable is non-private, but
if it's non-null, we extract the boolean value for the privacy mode
and store it in the transferable.
* It adds checks in debug builds to make sure that Init is always
called, in form of fatal assertions.
* It adds nsIDOMDocument* agruments to nsIClipboardHelper methods which
represent the document that the string is coming from.
nsIClipboardHelper implementation internally gets the nsILoadContext
from that and passes it on to the transferable upon creation. The
reason that I did this was that nsIClipboardHelper is supposed to be a
high-level helper, and in most of its call sites, we have easy access
to a document object.
* It modifies all of the call sites of the above interfaces according to
this change.
* It adds a GetLoadContext helper to nsIDocument to help with changing
the call sites.
When SeaMonkey switched to toolkit's nsDragAndDrop.js, it lost the dragDropSecurityCheck method, which for SM was on nsDragAndDrop, but for FF was on tabbrowser.
Moving that method from tabbrowser to toolkit's nsDragAndDrop.js, and cleaning it up a little.
