Update to Chromium version 70.0.3538.0 (#587811)

Known issues:
- The CefLoadCRLSetsFile function needs to be re-implemented (see issue #2497).
- Linux: GTK2 support has been removed. The cefclient sample needs to be updated
  to use GTK3 (see issue #2014).

libcef/browser/extensions/extension_web_contents_observer.h

@@ -38,7 +38,8 @@ class CefExtensionWebContentsObserver
 
   // Our content script observers. Declare at top so that it will outlive all
   // other members, since they might add themselves as observers.
-  base::ObserverList<ScriptExecutionObserver> script_execution_observers_;
+  base::ObserverList<ScriptExecutionObserver>::Unchecked
+      script_execution_observers_;
 
   std::unique_ptr<ScriptExecutor> script_executor_;