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/devtools/devtools_manager.cc

@@ -22,6 +22,10 @@ class CefDevToolsRegistrationImpl : public CefRegistration,
     DCHECK(observer_);
   }
 
+  CefDevToolsRegistrationImpl(const CefDevToolsRegistrationImpl&) = delete;
+  CefDevToolsRegistrationImpl& operator=(const CefDevToolsRegistrationImpl&) =
+      delete;
+
   ~CefDevToolsRegistrationImpl() override {
     CEF_REQUIRE_UIT();
 
@@ -88,7 +92,6 @@ class CefDevToolsRegistrationImpl : public CefRegistration,
   base::WeakPtr<CefDevToolsController> controller_;
 
   IMPLEMENT_REFCOUNTING_DELETE_ON_UIT(CefDevToolsRegistrationImpl);
-  DISALLOW_COPY_AND_ASSIGN(CefDevToolsRegistrationImpl);
 };
 
 }  // namespace