Bug 1337698 - Use UniquePtr instead of nsAutoPtr in editor

* PlaceholderTransaction should use UniquePtr
* HTMLEditor should use UniquePtr
* TypeInState should use UniquePtr

Tag #1375

editor/libeditor/HTMLEditor.cpp

@@ -287,7 +287,7 @@ HTMLEditor::Init(nsIDOMDocument* aDoc,
     }
 
     // Init the HTML-CSS utils
-    mCSSEditUtils = new CSSEditUtils(this);
+    mCSSEditUtils = MakeUnique<CSSEditUtils>(this);
 
     // disable links
     nsCOMPtr<nsIPresShell> presShell = GetPresShell();