Clarify devtools console log when a passive event listener is preventDefaulted.

Add a reference to the chromestatus entry regarding document level
passive event listeners.

BUG=627104

Review-Url: https://codereview.chromium.org/2272993004
Cr-Commit-Position: refs/heads/master@{#414462}

third_party/WebKit/Source/core/events/Event.cpp

@@ -80,8 +80,8 @@ Event::Event(const AtomicString& eventType, bool canBubbleArg, bool cancelableAr
     , m_cancelBubble(false)
     , m_wasInitialized(true)
     , m_isTrusted(false)
-    , m_handlingPassive(false)
     , m_preventDefaultCalledOnUncancelableEvent(false)
+    , m_handlingPassive(PassiveMode::NotPassive)
     , m_eventPhase(0)
     , m_currentTarget(nullptr)
     , m_platformTimeStamp(platformTimeStamp)
@@ -225,11 +225,26 @@ bool Event::isBeforeUnloadEvent() const
 
 void Event::preventDefault()
 {
-    if (m_handlingPassive) {
+    if (m_handlingPassive != PassiveMode::NotPassive) {
         m_preventDefaultCalledDuringPassive = true;
+
         const LocalDOMWindow* window = m_eventPath ? m_eventPath->windowEventContext().window() : 0;
-        if (window)
-            window->printErrorMessage("Unable to preventDefault inside passive event listener invocation.");
+        if (window) {
+            const char* devToolsMsg = nullptr;
+            switch (m_handlingPassive) {
+            case PassiveMode::NotPassive:
+                NOTREACHED();
+                break;
+            case PassiveMode::Passive:
+                devToolsMsg = "Unable to preventDefault inside passive event listener invocation.";
+                break;
+            case PassiveMode::PassiveForcedDocumentLevel:
+                devToolsMsg = "Unable to preventDefault inside passive event listener due to target being treated as passive. See https://www.chromestatus.com/features/5093566007214080";
+                break;
+            }
+            if (devToolsMsg)
+                window->printErrorMessage(devToolsMsg);
+        }
         return;
     }
 
@@ -281,9 +296,9 @@ HeapVector<Member<EventTarget>> Event::composedPath(ScriptState* scriptState) co
     return pathInternal(scriptState, EmptyAfterDispatch);
 }
 
-void Event::setHandlingPassive(bool value)
+void Event::setHandlingPassive(PassiveMode mode)
 {
-    m_handlingPassive = value;
+    m_handlingPassive = mode;
     m_preventDefaultCalledDuringPassive = false;
 }
 

third_party/WebKit/Source/core/events/Event.h

@@ -79,6 +79,12 @@ public:
         Scoped,
     };
 
+    enum class PassiveMode {
+        NotPassive,
+        Passive,
+        PassiveForcedDocumentLevel,
+    };
+
     static Event* create()
     {
         return new Event;
@@ -211,7 +217,7 @@ public:
     bool isTrusted() const { return m_isTrusted; }
     void setTrusted(bool value) { m_isTrusted = value; }
 
-    void setHandlingPassive(bool value);
+    void setHandlingPassive(PassiveMode);
 
     bool preventDefaultCalledDuringPassive() const { return m_preventDefaultCalledDuringPassive; }
 
@@ -230,6 +236,8 @@ protected:
 
     void setCanBubble(bool bubble) { m_canBubble = bubble; }
 
+    PassiveMode handlingPassive() const { return m_handlingPassive; }
+
 private:
 
     enum EventPathMode {
@@ -252,7 +260,6 @@ private:
     unsigned m_cancelBubble:1;
     unsigned m_wasInitialized:1;
     unsigned m_isTrusted : 1;
-    unsigned m_handlingPassive : 1;
 
     // Whether preventDefault was called when |m_handlingPassive| is
     // true. This field is reset on each call to setHandlingPassive.
@@ -260,6 +267,7 @@ private:
     // Whether preventDefault was called on uncancelable event.
     unsigned m_preventDefaultCalledOnUncancelableEvent : 1;
 
+    PassiveMode m_handlingPassive;
     unsigned short m_eventPhase;
     Member<EventTarget> m_currentTarget;
     Member<EventTarget> m_target;

third_party/WebKit/Source/core/events/EventTarget.cpp

@@ -65,6 +65,15 @@ enum PassiveForcedListenerResultType {
     PassiveForcedListenerResultTypeMax
 };
 
+Event::PassiveMode eventPassiveMode(const RegisteredEventListener& eventListener)
+{
+    if (!eventListener.passive())
+        return Event::PassiveMode::NotPassive;
+    if (eventListener.passiveForcedForDocumentTarget())
+        return Event::PassiveMode::PassiveForcedDocumentLevel;
+    return Event::PassiveMode::Passive;
+}
+
 Settings* windowSettings(LocalDOMWindow* executingWindow)
 {
     if (executingWindow) {
@@ -627,7 +636,7 @@ bool EventTarget::fireEventListeners(Event* event, EventTargetData* d, EventList
         if (event->immediatePropagationStopped())
             break;
 
-        event->setHandlingPassive(registeredListener.passive());
+        event->setHandlingPassive(eventPassiveMode(registeredListener));
         bool passiveForced = registeredListener.passiveForcedForDocumentTarget();
 
         InspectorInstrumentation::NativeBreakpoint nativeBreakpoint(context, this, event);
@@ -655,7 +664,7 @@ bool EventTarget::fireEventListeners(Event* event, EventTargetData* d, EventList
             passiveForcedHistogram.count(breakageType);
         }
 
-        event->setHandlingPassive(false);
+        event->setHandlingPassive(Event::PassiveMode::NotPassive);
 
         CHECK_LE(i, size);
     }

third_party/WebKit/Source/core/events/TouchEvent.cpp

@@ -204,7 +204,7 @@ void TouchEvent::preventDefault()
     // A common developer error is to wait too long before attempting to stop
     // scrolling by consuming a touchmove event. Generate a warning if this
     // event is uncancelable.
-    if (!cancelable() && view() && view()->isLocalDOMWindow() && view()->frame()) {
+    if (!cancelable() && handlingPassive() == PassiveMode::NotPassive && view() && view()->isLocalDOMWindow() && view()->frame()) {
         toLocalDOMWindow(view())->frame()->console().addMessage(ConsoleMessage::create(JSMessageSource, WarningMessageLevel,
             "Ignored attempt to cancel a " + type() + " event with cancelable=false, for example because scrolling is in progress and cannot be interrupted."));
     }