Bug 1452751 - add a pref to control whether to default to passive touch listeners on window/document/documentElement/body , r=kats

--HG--
extra : rebase_source : ba015d60e7ab7da183048dc59dfb0fe42930df6d

dom/events/EventListenerManager.cpp

@@ -686,6 +686,21 @@ EventListenerManager::ListenerCanHandle(const Listener* aListener,
   return aListener->mEventMessage == aEventMessage;
 }
 
+static bool
+DefaultToPassiveTouchListeners()
+{
+  static bool sDefaultToPassiveTouchListeners = false;
+  static bool sIsPrefCached = false;
+
+  if (!sIsPrefCached) {
+    sIsPrefCached = true;
+    Preferences::AddBoolVarCache(&sDefaultToPassiveTouchListeners,
+                                 "dom.event.default_to_passive_touch_listeners");
+  }
+
+  return sDefaultToPassiveTouchListeners;
+}
+
 void
 EventListenerManager::AddEventListenerByType(
                         EventListenerHolder aListenerHolder,
@@ -702,7 +717,8 @@ EventListenerManager::AddEventListenerByType(
   EventListenerFlags flags = aFlags;
   if (aPassive.WasPassed()) {
     flags.mPassive = aPassive.Value();
-  } else if (message == eTouchStart || message == eTouchMove) {
+  } else if ((message == eTouchStart || message == eTouchMove) &&
+             mIsMainThreadELM && DefaultToPassiveTouchListeners()) {
     nsCOMPtr<nsINode> node;
     nsCOMPtr<nsPIDOMWindowInner> win;
     if ((win = GetTargetAsInnerWindow()) ||

gfx/layers/apz/test/mochitest/test_group_touchevents.html

@@ -76,7 +76,8 @@ var subtests = [
                                                 ["apz.test.fails_with_native_injection", isWindows]]},
 
   {'file': 'helper_tap_default_passive.html', 'prefs': [["apz.content_response_timeout", 24 * 60 * 60 * 1000],
-                                                        ["apz.test.fails_with_native_injection", isWindows]]},
+                                                        ["apz.test.fails_with_native_injection", isWindows],
+                                                        ["dom.event.default_to_passive_touch_listeners", true]]},
 
   // Simple test to exercise touch-action CSS property
   {'file': 'helper_touch_action.html', 'prefs': touch_action_prefs},

modules/libpref/init/all.js

@@ -5917,3 +5917,7 @@ pref("layers.omtp.dump-capture", false);
 // a content to view.  This is mostly intended to prevent infinite
 // loops with faulty converters involved.
 pref("general.document_open_conversion_depth_limit", 20);
+
+// If true, touchstart and touchmove listeners on window, document,
+// documentElement and document.body are passive by default.
+pref("dom.event.default_to_passive_touch_listeners", false);