Bug 1650607 - Do not replace / with : in File constructor. r=baku

Basically a backout of https://hg.mozilla.org/mozilla-central/rev/1857e763332c.
Pending spec change: w3c/FileAPI#41

Differential Revision: https://phabricator.services.mozilla.com/D86981

dom/file/File.cpp

@@ -135,11 +135,7 @@ already_AddRefed<File> File::Constructor(const GlobalObject& aGlobal,
                                          const nsAString& aName,
                                          const FilePropertyBag& aBag,
                                          ErrorResult& aRv) {
-  // Normalizing the filename
-  nsString name(aName);
-  name.ReplaceChar('/', ':');
-
-  RefPtr<MultipartBlobImpl> impl = new MultipartBlobImpl(name);
+  RefPtr<MultipartBlobImpl> impl = new MultipartBlobImpl(aName);
 
   nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(aGlobal.GetAsSupports());
   MOZ_ASSERT(global);