Bug 1210057. Schedule a paint when an apz aware event listener is added so that event regions on the layer tree get updated. r=smaug

dom/events/EventListenerManager.cpp

@@ -48,6 +48,7 @@
 #include "nsPIDOMWindow.h"
 #include "nsSandboxFlags.h"
 #include "xpcpublic.h"
+#include "nsIFrame.h"
 
 namespace mozilla {
 
@@ -416,10 +417,7 @@ EventListenerManager::AddEventListenerInternal(
   }
 
   if (IsApzAwareEvent(aTypeAtom)) {
-    nsCOMPtr<nsINode> node = do_QueryInterface(mTarget);
-    if (node) {
-      node->SetMayHaveApzAwareListeners();
-    }
+    ProcessApzAwareEventListenerAdd();
   }
 
   if (aTypeAtom && mTarget) {
@@ -432,6 +430,44 @@ EventListenerManager::AddEventListenerInternal(
   }
 }
 
+void
+EventListenerManager::ProcessApzAwareEventListenerAdd()
+{
+  // Mark the node as having apz aware listeners
+  nsCOMPtr<nsINode> node = do_QueryInterface(mTarget);
+  if (node) {
+    node->SetMayHaveApzAwareListeners();
+  }
+
+  // Schedule a paint so event regions on the layer tree gets updated
+  nsIDocument* doc = nullptr;
+  if (node) {
+    doc = node->OwnerDoc();
+  }
+  if (!doc) {
+    if (nsCOMPtr<nsPIDOMWindowInner> window = GetTargetAsInnerWindow()) {
+      doc = window->GetExtantDoc();
+    }
+  }
+  if (!doc) {
+    if (nsCOMPtr<DOMEventTargetHelper> helper = do_QueryInterface(mTarget)) {
+      if (nsPIDOMWindowInner* window = helper->GetOwner()) {
+        doc = window->GetExtantDoc();
+      }
+    }
+  }
+
+  if (doc) {
+    nsIPresShell* ps = doc->GetShell();
+    if (ps) {
+      nsIFrame* f = ps->GetRootFrame();
+      if (f) {
+        f->SchedulePaint();
+      }
+    }
+  }
+}
+
 bool
 EventListenerManager::IsDeviceType(EventMessage aEventMessage)
 {

dom/events/EventListenerManager.h

@@ -467,6 +467,8 @@ protected:
 
   nsIDocShell* GetDocShellForTarget();
 
+  void ProcessApzAwareEventListenerAdd();
+
   /**
    * Compile the "inline" event listener for aListener.  The
    * body of the listener can be provided in aBody; if this is null we