Bug 1253052. Only schedule paint when apz aware event listener is added if event regions/apz are enabled. r=kats

Bug 1210057 added this, we should only do it if apz/event regions are enabled.

dom/events/EventListenerManager.cpp

@@ -49,6 +49,7 @@
 #include "nsSandboxFlags.h"
 #include "xpcpublic.h"
 #include "nsIFrame.h"
+#include "nsDisplayList.h"
 
 namespace mozilla {
 
@@ -457,7 +458,7 @@ EventListenerManager::ProcessApzAwareEventListenerAdd()
     }
   }
 
-  if (doc) {
+  if (doc && nsDisplayListBuilder::LayerEventRegionsEnabled()) {
     nsIPresShell* ps = doc->GetShell();
     if (ps) {
       nsIFrame* f = ps->GetRootFrame();

layout/base/nsDisplayList.cpp

@@ -1420,14 +1420,25 @@ bool
 nsDisplayListBuilder::IsBuildingLayerEventRegions()
 {
   if (mMode == PAINTING) {
-    // Note: this is the only place that gets to query LayoutEventRegionsEnabled
-    // 'directly' - other code should call this function.
+    // Note: this function and LayerEventRegionsEnabled are the only places
+    // that get to query LayoutEventRegionsEnabled 'directly' - other code
+    // should call this function.
     return gfxPrefs::LayoutEventRegionsEnabledDoNotUseDirectly() ||
            mAsyncPanZoomEnabled;
   }
   return false;
 }
 
+/* static */ bool
+nsDisplayListBuilder::LayerEventRegionsEnabled()
+{
+  // Note: this function and IsBuildingLayerEventRegions are the only places
+  // that get to query LayoutEventRegionsEnabled 'directly' - other code
+  // should call this function.
+  return gfxPrefs::LayoutEventRegionsEnabledDoNotUseDirectly() ||
+         gfxPlatform::AsyncPanZoomEnabled();
+}
+
 void nsDisplayListSet::MoveTo(const nsDisplayListSet& aDestination) const
 {
   aDestination.BorderBackground()->AppendToTop(BorderBackground());

layout/base/nsDisplayList.h

@@ -435,6 +435,7 @@ public:
     mLayerEventRegions = aItem;
   }
   bool IsBuildingLayerEventRegions();
+  static bool LayerEventRegionsEnabled();
   bool IsInsidePointerEventsNoneDoc()
   {
     return CurrentPresShellState()->mInsidePointerEventsNoneDoc;