Bug 1181424 - Add pref nglayout.debug.invalidation to all.js. r=mattwoodrow

By doing so, we can easily toggle this preference in about:config.

--HG--
extra : commitid : thKwTBeMbT

modules/libpref/init/all.js

@@ -907,6 +907,9 @@ pref("nglayout.debug.paint_flashing_chrome", false);
 // BasicLayers (other layer managers always update the entire widget area)
 pref("nglayout.debug.widget_update_flashing", false);
 
+// Enable/disable display list invalidation logging --- useful for debugging.
+pref("nglayout.debug.invalidation", false);
+
 // Whether image visibility is enabled globally (ie we will try to unlock images
 // that are not visible).
 pref("layout.imagevisibility.enabled", true);