Bug 1305957 part 1 - Add 'layout.scroll-anchoring.enabled' preference behind nightly flag. r=hiro

Differential Revision: https://phabricator.services.mozilla.com/D13263

--HG--
extra : rebase_source : cc33b22252dae023a904ea7dd26117e1d70a92dc
extra : histedit_source : f4fad5a2180bad4af9e42470bd9b0a51d8c5bdab

modules/libpref/init/StaticPrefList.h

@@ -883,6 +883,19 @@ VARCACHE_PREF(
   bool, true
 )
 
+// Pref to control enabling scroll anchoring.
+#ifdef NIGHTLY_BUILD
+#define PREF_VALUE true
+#else
+#define PREF_VALUE false
+#endif
+VARCACHE_PREF(
+  "layout.css.scroll-anchoring.enabled",
+   layout_css_scroll_anchoring_enabled,
+  bool, PREF_VALUE
+)
+#undef PREF_VALUE
+
 //---------------------------------------------------------------------------
 // JavaScript prefs
 //---------------------------------------------------------------------------