Log when PreventDefaulting event forced uncancellable.

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

Index: third_party/WebKit/Source/core/events/TouchEvent.cpp
diff --git a/third_party/WebKit/Source/core/events/TouchEvent.cpp b/third_party/WebKit/Source/core/events/TouchEvent.cpp
index 066d2c9db8dbecbd529dc828fd56e07c39c97779..d8fbe16ed16f51d6bd72da3fb1214ae40f5b2310 100644
--- a/third_party/WebKit/Source/core/events/TouchEvent.cpp
+++ b/third_party/WebKit/Source/core/events/TouchEvent.cpp
@@ -253,15 +253,37 @@ 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.
+  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:
@@ -269,6 +291,7 @@ void TouchEvent::preventDefault() {
       // 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 "
@@ -282,7 +305,7 @@ void TouchEvent::preventDefault() {
   if (!warningMessage.isEmpty() && view() && view()->isLocalDOMWindow() &&
       view()->frame()) {
     toLocalDOMWindow(view())->frame()->console().addMessage(
-        ConsoleMessage::create(JSMessageSource, WarningMessageLevel,
+        ConsoleMessage::create(messageSource, WarningMessageLevel,
                                warningMessage));
   }