Bug 1565668 - Add an off-by-default preference called gfx.core-animation.enabled. r=jrmuizel

This preference doesn't do anything yet but having it at this point in the
patch stack lets me untangle things a bit.

Differential Revision: https://phabricator.services.mozilla.com/D37914

--HG--
extra : moz-landing-system : lando

modules/libpref/init/StaticPrefList.h

@@ -3171,6 +3171,13 @@ VARCACHE_PREF(
   RelaxedAtomicBool, false
 )
 
+VARCACHE_PREF(
+  Once,
+  "gfx.core-animation.enabled",
+  gfx_core_animation_enabled,
+  bool, false
+)
+
 #if defined(MOZ_WIDGET_ANDROID)
 // Overrides the glClear color used when the surface origin is not (0, 0)
 // Used for drawing a border around the content.

modules/libpref/init/all.js

@@ -741,6 +741,7 @@ pref("gfx.webrender.program-binary-disk", true);
 
 #ifdef XP_MACOSX
 pref("gfx.compositor.glcontext.opaque", false);
+pref("gfx.core-animation.enabled", false);
 #endif
 
 pref("gfx.webrender.highlight-painted-layers", false);