Bug 1518405 - Turn on picture caching in webrender. r=jrmuizel

Differential Revision: https://phabricator.services.mozilla.com/D16740

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

modules/libpref/init/all.js

@@ -963,7 +963,7 @@ pref("gfx.webrender.debug.show-overdraw", false);
 pref("gfx.webrender.debug.slow-frame-indicator", false);
 pref("gfx.webrender.dl.dump-parent", false);
 pref("gfx.webrender.dl.dump-content", false);
-pref("gfx.webrender.picture-caching", false);
+pref("gfx.webrender.picture-caching", true);
 
 #ifdef EARLY_BETA_OR_EARLIER
 pref("performance.adjust_to_machine", true);