Revert "WPF/WinForms/OffScreen - Enable Chromium Site Isolation"

This reverts commit 2366912.

Author: amaitland

CefSharp.Core.Runtime/CefSettingsBase.h

@@ -49,6 +49,11 @@ namespace CefSharp
                 _cefCustomSchemes = gcnew List<CefCustomScheme^>();
                 _cefCommandLineArgs = gcnew CommandLineArgDictionary();
 
+                //Disable site isolation trials as this causes problems with frames
+                //being hosted in different render processes.
+                //https://github.com/cefsharp/CefSharp/issues/2967
+                _cefCommandLineArgs->Add("disable-site-isolation-trials");
+
                 //Disable Windows Spellchecker as CEF doesn't support yet
                 //https://bitbucket.org/chromiumembedded/cef/issues/3055/windows-spell-checker-not-working-add
                 _cefCommandLineArgs->Add("disable-features", "CalculateNativeWinOcclusion,WinUseBrowserSpellChecker");