Bug 1497916 - Ensure the WR qualified pref is only enabled on nightly. r=jrmuizel

Differential Revision: https://phabricator.services.mozilla.com/D8248

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

gfx/thebes/gfxPrefs.h

@@ -520,7 +520,11 @@ private:
   DECL_GFX_PREF(Once, "gfx.vsync.compositor.unobserve-count",  CompositorUnobserveCount, int32_t, 10);
 
   DECL_GFX_PREF(Once, "gfx.webrender.all",                     WebRenderAll, bool, false);
+#ifdef NIGHTLY_BUILD
   DECL_GFX_PREF(Once, "gfx.webrender.all.qualified",           WebRenderAllQualified, bool, true);
+#else
+  DECL_GFX_PREF(Once, "gfx.webrender.all.qualified",           WebRenderAllQualified, bool, false);
+#endif
   DECL_GFX_PREF(Live, "gfx.webrender.blob-images",             WebRenderBlobImages, bool, true);
   DECL_GFX_PREF(Live, "gfx.webrender.blob.invalidation",       WebRenderBlobInvalidation, bool, false);
   DECL_GFX_PREF(Live, "gfx.webrender.blob.paint-flashing",     WebRenderBlobPaintFlashing, bool, false);