Bug 1819769 - don't dispatch a11y related events when there are no listeners, r=masayuki

Differential Revision: https://phabricator.services.mozilla.com/D175016

dom/base/nsContentUtils.cpp

@@ -466,6 +466,9 @@ nsParser* nsContentUtils::sXMLFragmentParser = nullptr;
 nsIFragmentContentSink* nsContentUtils::sXMLFragmentSink = nullptr;
 bool nsContentUtils::sFragmentParsingActive = false;
 
+bool nsContentUtils::sMayHaveFormCheckboxStateChangeListeners = false;
+bool nsContentUtils::sMayHaveFormRadioStateChangeListeners = false;
+
 mozilla::LazyLogModule nsContentUtils::gResistFingerprintingLog(
     "nsResistFingerprinting");
 mozilla::LazyLogModule nsContentUtils::sDOMDumpLog("Dump");

dom/base/nsContentUtils.h

@@ -3373,6 +3373,22 @@ class nsContentUtils {
    */
   static void RequestGeckoTaskBurst();
 
+  static void SetMayHaveFormCheckboxStateChangeListeners() {
+    sMayHaveFormCheckboxStateChangeListeners = true;
+  }
+
+  static bool MayHaveFormCheckboxStateChangeListeners() {
+    return sMayHaveFormCheckboxStateChangeListeners;
+  }
+
+  static void SetMayHaveFormRadioStateChangeListeners() {
+    sMayHaveFormRadioStateChangeListeners = true;
+  }
+
+  static bool MayHaveFormRadioStateChangeListeners() {
+    return sMayHaveFormRadioStateChangeListeners;
+  }
+
  private:
   static bool InitializeEventTable();
 
@@ -3493,6 +3509,9 @@ class nsContentUtils {
 
   static int32_t sInnerOrOuterWindowCount;
   static uint32_t sInnerOrOuterWindowSerialCounter;
+
+  static bool sMayHaveFormCheckboxStateChangeListeners;
+  static bool sMayHaveFormRadioStateChangeListeners;
 };
 
 /* static */ inline ExtContentPolicyType

dom/events/EventListenerManager.cpp

@@ -472,6 +472,12 @@ void EventListenerManager::AddEventListenerInternal(
           window->SetHasTransitionEventListeners();
         }
         break;
+      case eFormCheckboxStateChange:
+        nsContentUtils::SetMayHaveFormCheckboxStateChangeListeners();
+        break;
+      case eFormRadioStateChange:
+        nsContentUtils::SetMayHaveFormRadioStateChangeListeners();
+        break;
       default:
         // XXX Use NS_ASSERTION here to print resolvedEventMessage since
         //     MOZ_ASSERT can take only string literal, not pointer to

dom/html/HTMLInputElement.cpp

@@ -3728,8 +3728,10 @@ nsresult HTMLInputElement::PostHandleEvent(EventChainPostVisitor& aVisitor) {
 #ifdef ACCESSIBILITY
       // Fire an event to notify accessibility
       if (mType == FormControlType::InputCheckbox) {
-        FireEventForAccessibility(this, eFormCheckboxStateChange);
-      } else {
+        if (nsContentUtils::MayHaveFormCheckboxStateChangeListeners()) {
+          FireEventForAccessibility(this, eFormCheckboxStateChange);
+        }
+      } else if (nsContentUtils::MayHaveFormRadioStateChangeListeners()) {
         FireEventForAccessibility(this, eFormRadioStateChange);
         // Fire event for the previous selected radio.
         nsCOMPtr<nsIContent> content = do_QueryInterface(aVisitor.mItemData);