Log when PreventDefaulting event forced uncancellable.

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

 /*
  * Copyright 2008, The Android Open Source Project
  * Copyright (C) 2012 Research In Motion Limited. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *  * Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  *  * Redistributions in binary form must reproduce the above copyright
@@ skipping 235 matching lines @@
 bool TouchEvent::isTouchEvent() const {
   return true;
 }
 
 void TouchEvent::preventDefault() {
   UIEventWithKeyState::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.
+  MessageSource messageSource = JSMessageSource;
   String warningMessage;
   switch (handlingPassive()) {
     case PassiveMode::NotPassive:
     case PassiveMode::NotPassiveDefault:
       if (!cancelable()) {
-        warningMessage = "Ignored attempt to cancel a " + type() +
-                         " event with cancelable=false, for example "
-                         "because scrolling is in progress and "
-                         "cannot be interrupted.";
+        UseCounter::count(view()->frame(),
+                          UseCounter::UncancellableTouchEventPreventDefaulted);
+
+        if (m_nativeEvent &&
+            m_nativeEvent->dispatchType ==
+                WebInputEvent::
+                    ListenersForcedNonBlockingDueToMainThreadResponsiveness) {
+          // Non blocking due to main thread responsiveness.
+          UseCounter::count(
+              view()->frame(),
+              UseCounter::
+                  UncancellableTouchEventDueToMainThreadResponsivenessPreventDefaulted);
+          messageSource = InterventionMessageSource;
+          warningMessage =
+              "Ignored attempt to cancel a " + type() +
+              " event with cancelable=false. This event was forced to be "
+              "non-cancellable because the page was too busy to handle the "
+              "event promptly.";
+        } else {
+          // Non blocking for any other reason.
+          warningMessage = "Ignored attempt to cancel a " + type() +

[bokan, 2017/02/10 00:24:06]

Just checking - you intend for the ForcedNonBlockingDueToFling to use this
warning too (and not be counted in "ForcedNonBlocking" for the use counter)?

[tdresser, 2017/02/10 13:24:57]

We consider the "due to fling case" to be equivalent to other cases where we
force the event non blocking because we're mid scroll, so we don't call it out
separately.

[bokan, 2017/02/10 15:36:16]

Acknowledged.

+                           " event with cancelable=false, for example "
+                           "because scrolling is in progress and "
+                           "cannot be interrupted.";
+        }
       }
       break;
     case PassiveMode::PassiveForcedDocumentLevel:
       // Only enable the warning when the current touch action is auto because
       // an author may use touch action but call preventDefault for interop with
       // browsers that don't support touch-action.
       if (m_currentTouchAction == TouchActionAuto) {
+        messageSource = InterventionMessageSource;
         warningMessage =
             "Unable to preventDefault inside passive event listener due to "
             "target being treated as passive. See "
             "https://www.chromestatus.com/features/5093566007214080";
       }
       break;
     default:
       break;
   }
 
   if (!warningMessage.isEmpty() && view() && view()->isLocalDOMWindow() &&
       view()->frame()) {
     toLocalDOMWindow(view())->frame()->console().addMessage(
-        ConsoleMessage::create(JSMessageSource, WarningMessageLevel,
+        ConsoleMessage::create(messageSource, WarningMessageLevel,
                                warningMessage));
   }
 
   if ((type() == EventTypeNames::touchstart ||
        type() == EventTypeNames::touchmove) &&
       view() && view()->frame() && m_currentTouchAction == TouchActionAuto) {
     switch (handlingPassive()) {
       case PassiveMode::NotPassiveDefault:
         UseCounter::count(view()->frame(),
                           UseCounter::TouchEventPreventedNoTouchAction);
@@ skipping 52 matching lines @@
   return toTouchEvent(EventDispatchMediator::event());
 }
 
 DispatchEventResult TouchEventDispatchMediator::dispatchEvent(
     EventDispatcher& dispatcher) const {
   event().eventPath().adjustForTouchEvent(event());
   return dispatcher.dispatch();
 }
 
 }  // namespace blink