Bug 1517241 - Rename nsIDocument to mozilla::dom::Document. r=smaug

Summary: Really sorry for the size of the patch. It's mostly automatic
s/nsIDocument/Document/ but I had to fix up in a bunch of places manually to
add the right namespacing and such.

Overall it's not a very interesting patch I think.

nsDocument.cpp turns into Document.cpp, nsIDocument.h into Document.h and
nsIDocumentInlines.h into DocumentInlines.h.

I also changed a bunch of nsCOMPtr usage to RefPtr, but not all of it.

While fixing up some of the bits I also removed some unneeded OwnerDoc() null
checks and such, but I didn't do anything riskier than that.

dom/html/HTMLAreaElement.cpp

@@ -66,15 +66,14 @@ nsDOMTokenList* HTMLAreaElement::RelList() {
   return mRelList;
 }
 
-nsresult HTMLAreaElement::BindToTree(nsIDocument* aDocument,
-                                     nsIContent* aParent,
+nsresult HTMLAreaElement::BindToTree(Document* aDocument, nsIContent* aParent,
                                      nsIContent* aBindingParent) {
   Link::ResetLinkState(false, Link::ElementHasHref());
   nsresult rv =
       nsGenericHTMLElement::BindToTree(aDocument, aParent, aBindingParent);
   NS_ENSURE_SUCCESS(rv, rv);
 
-  nsIDocument* doc = GetComposedDoc();
+  Document* doc = GetComposedDoc();
   if (doc) {
     doc->RegisterPendingLinkUpdate(this);
   }