Implement "cookie-averse document objects".

See: https://html.spec.whatwg.org/multipage/dom.html#cookie-averse-document-object
This resolves #196.

dom/base/nsContentSink.cpp

@@ -305,6 +305,11 @@ nsContentSink::ProcessHeaderData(nsIAtom* aHeader, const nsAString& aValue,
   mDocument->SetHeaderData(aHeader, aValue);
 
   if (aHeader == nsGkAtoms::setcookie) {
+    // Don't allow setting cookies in cookie-averse documents.
+    if (mDocument->IsCookieAverse()) {
+      return NS_OK;
+    }
+
     // Note: Necko already handles cookies set via the channel.  We can't just
     // call SetCookie on the channel because we want to do some security checks
     // here.

dom/base/nsIDocument.h

@@ -1923,6 +1923,34 @@ public:
     return mMarkedCCGeneration;
   }
 
+  /**
+   * Returns whether this document is cookie-averse. See
+   * https://html.spec.whatwg.org/multipage/dom.html#cookie-averse-document-object
+   */
+  bool IsCookieAverse() const
+  {
+    // If we are a document that "has no browsing context."
+    if (!GetInnerWindow()) {
+      return true;
+    }
+
+    // If we are a document "whose URL's scheme is not a network scheme."
+    // NB: Explicitly allow file: URIs to store cookies.
+    nsCOMPtr<nsIURI> codebaseURI;
+    NodePrincipal()->GetURI(getter_AddRefs(codebaseURI));
+
+    if (!codebaseURI) {
+      return true;
+    }
+
+    nsAutoCString scheme;
+    codebaseURI->GetScheme(scheme);
+    return !scheme.EqualsLiteral("http") &&
+           !scheme.EqualsLiteral("https") &&
+           !scheme.EqualsLiteral("ftp") &&
+           !scheme.EqualsLiteral("file");
+  }
+
   bool IsLoadedAsData()
   {
     return mLoadedAsData;

dom/html/nsHTMLDocument.cpp

@@ -1255,6 +1255,11 @@ nsHTMLDocument::GetCookie(nsAString& aCookie, ErrorResult& rv)
     rv.Throw(NS_ERROR_DOM_SECURITY_ERR);
     return;
   }
+
+  // If the document is a cookie-averse document, return an empty string.
+  if (IsCookieAverse()) {
+    return;
+  }
   
   // not having a cookie service isn't an error
   nsCOMPtr<nsICookieService> service = do_GetService(NS_COOKIESERVICE_CONTRACTID);
@@ -1310,6 +1315,11 @@ nsHTMLDocument::SetCookie(const nsAString& aCookie, ErrorResult& rv)
     return;
   }
 
+  // If the document is a cookie-averse document, do nothing.
+  if (IsCookieAverse()) {
+    return;
+  }
+
   // not having a cookie service isn't an error
   nsCOMPtr<nsICookieService> service = do_GetService(NS_COOKIESERVICE_CONTRACTID);
   if (service && mDocumentURI) {