Remove DISALLOW_ macro from libcef/ (see issue #3234)

Also perform related C++ cleanup:
- Use =default instead of {} for default implementations of
  constructors/destructors.
- Replace typedef with using.

libcef/browser/browser_contents_delegate.h

@@ -72,6 +72,10 @@ class CefBrowserContentsDelegate : public content::WebContentsDelegate,
   explicit CefBrowserContentsDelegate(
       scoped_refptr<CefBrowserInfo> browser_info);
 
+  CefBrowserContentsDelegate(const CefBrowserContentsDelegate&) = delete;
+  CefBrowserContentsDelegate& operator=(const CefBrowserContentsDelegate&) =
+      delete;
+
   void ObserveWebContents(content::WebContents* new_contents);
 
   // Manage observer objects. The observer must either outlive this object or
@@ -195,8 +199,6 @@ class CefBrowserContentsDelegate : public content::WebContentsDelegate,
 
   // True if the focus is currently on an editable field on the page.
   bool focus_on_editable_field_ = false;
-
-  DISALLOW_COPY_AND_ASSIGN(CefBrowserContentsDelegate);
 };
 
 #endif  // CEF_LIBCEF_BROWSER_BROWSER_CONTENTS_DELEGATE_H_