Bug 1432272 Make Fetch API use the global's base URL instead of the entry document's base URL. r=bz

The fetch spec used to use the entry settings as the base for parsing relative
Request/Response URL's, but this is no longer the case.  This was changed in:

whatwg/fetch#367

Update our code to match this behavior.  We basically convert GetEntryDocument()
to QI the global to nsGlobalWindowInner and use its ExtantDoc instead.

No changes are needed for workers since its not possible to perform cross-global
javascript access in worker threads.

UltraBlame original commit: b5432554c7bd39dd14adff8060a7f7757bb2c40e

Author: marco-c

dom/fetch/Request.cpp

@@ -319,7 +319,8 @@ Request::Constructor(const GlobalObject& aGlobal,
     nsAutoString requestURL;
     nsCString fragment;
     if (NS_IsMainThread()) {
-      nsIDocument* doc = GetEntryDocument();
+      nsCOMPtr<nsPIDOMWindowInner> inner(do_QueryInterface(global));
+      nsIDocument* doc = inner ? inner->GetExtantDoc() : nullptr;
       if (doc) {
         GetRequestURLFromDocument(doc, input, requestURL, fragment, aRv);
       } else {
@@ -368,7 +369,8 @@ Request::Constructor(const GlobalObject& aGlobal,
     } else {
       nsAutoString referrerURL;
       if (NS_IsMainThread()) {
-        nsIDocument* doc = GetEntryDocument();
+        nsCOMPtr<nsPIDOMWindowInner> inner(do_QueryInterface(global));
+        nsIDocument* doc = inner ? inner->GetExtantDoc() : nullptr;
         nsCOMPtr<nsIURI> uri;
         if (doc) {
           uri = ParseURLFromDocument(doc, referrer, aRv);

dom/fetch/Response.cpp

@@ -100,7 +100,8 @@ Response::Redirect(const GlobalObject& aGlobal, const nsAString& aUrl,
 
   if (NS_IsMainThread()) {
     nsCOMPtr<nsIURI> baseURI;
-    nsIDocument* doc = GetEntryDocument();
+    nsCOMPtr<nsPIDOMWindowInner> inner(do_QueryInterface(aGlobal.GetAsSupports()));
+    nsIDocument* doc = inner ? inner->GetExtantDoc() : nullptr;
     if (doc) {
       baseURI = doc->GetBaseURI();
     }