Bug 1413546 - Fix e10s logic in nsLayoutUtils::AreRetainedDisplayListsEnabled() and set layout.display-list.retain.chrome to true r=mattwoodrow

Differential Revision: https://phabricator.services.mozilla.com/D2953

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

layout/base/nsLayoutUtils.cpp

@@ -468,9 +468,14 @@ nsLayoutUtils::AreRetainedDisplayListsEnabled()
 {
   if (XRE_IsContentProcess()) {
     return gfxPrefs::LayoutRetainDisplayList();
-  } else {
+  }
+
+  if (XRE_IsE10sParentProcess()) {
     return gfxPrefs::LayoutRetainDisplayListChrome();
   }
+
+  // Retained display lists require e10s.
+  return false;
 }
 
 bool

modules/libpref/init/all.js

@@ -3077,10 +3077,10 @@ pref("layout.display-list.dump-parent", false);
 // Toggle retaining display lists between paints
 #if !defined(ANDROID)
 pref("layout.display-list.retain", true);
+pref("layout.display-list.retain.chrome", true);
 #else
 pref("layout.display-list.retain", false);
 #endif
-pref("layout.display-list.retain.chrome", false);
 
 // Set the maximum amount of modified frames allowed before doing a full
 // display list rebuild.