Fixing build bustage on Linux

dom/public/base/nsPIDOMWindow.h

@@ -29,6 +29,8 @@
 #include "nsIScriptContext.h"
 #include "nsIDOMLocation.h"
 
+class nsIWebShell;
+
 #define NS_PIDOMWINDOW_IID \
 { 0x3aa80781, 0x7e6a, 0x11d3, { 0xbf, 0x87, 0x0, 0x10, 0x5a, 0x1b, 0x6, 0x27 } }