Add NS_TIMER import/export macros.

xpcom/base/nscore.h

@@ -134,6 +134,12 @@ typedef PRUint16 PRUnichar;
 #define NS_GFX_(type) NS_IMPORT_(type)
 #endif
 
+#ifdef _IMPL_NS_TIMER
+#define NS_TIMER NS_EXPORT
+#else
+#define NS_TIMER NS_IMPORT
+#endif
+
 #ifdef _IMPL_NS_PLUGIN
 #define NS_PLUGIN NS_EXPORT
 #else