Added TabbedBrowser2 demo for Linux

Update the TCEFBitmapBitBuffer size instead of destrying and creating it when the browser is resized.

demos/Lazarus_Linux/TabbedBrowser2/interfaces.pas

@@ -0,0 +1,30 @@
+unit Interfaces;
+
+{$mode objfpc}{$H+}
+
+interface
+
+{$IFDEF UNIX}{$IFNDEF DisableCWString}uses cwstring;{$ENDIF}{$ENDIF}
+
+procedure CustomWidgetSetInitialization;
+procedure CustomWidgetSetFinalization;
+
+implementation
+
+uses
+ {$IFNDEF EnableLibOverlay}
+ gtk2DisableLibOverlay,
+ {$ENDIF}
+ Gtk2Int, Forms;
+
+procedure CustomWidgetSetInitialization;
+begin
+  CreateWidgetset(TGtk2WidgetSet);
+end;
+
+procedure CustomWidgetSetFinalization;
+begin
+  FreeWidgetSet;
+end;
+
+end.