Bug 1537667. Allow the 'layout.display-list.retain' pref to work on android. r=mattwoodrow

Fennec isn't e10s, so neither existing check worked.

https://phabricator.services.mozilla.com/D24310

Differential Revision: https://phabricator.services.mozilla.com/D24428

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

layout/base/nsLayoutUtils.cpp

@@ -460,6 +460,9 @@ bool nsLayoutUtils::IsAnimationLoggingEnabled() {
 }
 
 bool nsLayoutUtils::AreRetainedDisplayListsEnabled() {
+#ifdef MOZ_WIDGET_ANDROID
+  return gfxPrefs::LayoutRetainDisplayList();;
+#else
   if (XRE_IsContentProcess()) {
     return gfxPrefs::LayoutRetainDisplayList();
   }
@@ -470,6 +473,7 @@ bool nsLayoutUtils::AreRetainedDisplayListsEnabled() {
 
   // Retained display lists require e10s.
   return false;
+#endif
 }
 
 bool nsLayoutUtils::DisplayRootHasRetainedDisplayListBuilder(nsIFrame* aFrame) {