Add UMA metrics for root scroller intervention to track forcing passive breakage.

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

 /*
  * Copyright (C) 2001 Peter Kelly (pmk@post.com)
  * Copyright (C) 2001 Tobias Anton (anton@stud.fbi.fh-darmstadt.de)
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 196 matching lines @@
 
     // Events that must not leak across isolated world, similar to how
     // ErrorEvent behaves, can override this method.
     virtual bool canBeDispatchedInWorld(const DOMWrapperWorld&) const { return true; }
 
     virtual EventDispatchMediator* createMediator();
 
     bool isTrusted() const { return m_isTrusted; }
     void setTrusted(bool value) { m_isTrusted = value; }
 
-    void setHandlingPassive(bool value) { m_handlingPassive = value; }
+    void setHandlingPassive(bool value);
+
+    bool preventDefaultCalledDuringPassive() const { return m_preventDefaultCalledDuringPassive; }
 
     DECLARE_VIRTUAL_TRACE();
 
 protected:
     Event();
     Event(const AtomicString& type, bool canBubble, bool cancelable, ComposedMode, double platformTimeStamp);
     Event(const AtomicString& type, bool canBubble, bool cancelable, double platformTimeStamp);
     Event(const AtomicString& type, bool canBubble, bool cancelable, ComposedMode = ComposedMode::Scoped);
     Event(const AtomicString& type, const EventInit&);
 
@@ skipping 18 matching lines @@
 
     unsigned m_propagationStopped:1;
     unsigned m_immediatePropagationStopped:1;
     unsigned m_defaultPrevented:1;
     unsigned m_defaultHandled:1;
     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.
+    unsigned m_preventDefaultCalledDuringPassive : 1;
+
     unsigned short m_eventPhase;
     Member<EventTarget> m_currentTarget;
     Member<EventTarget> m_target;
     DOMTimeStamp m_createTime;
     Member<Event> m_underlyingEvent;
     Member<EventPath> m_eventPath;
     // The monotonic platform time in seconds, for input events it is the
     // event timestamp provided by the host OS and reported in the original
     // WebInputEvent instance.
     double m_platformTimeStamp;
 };
 
 #define DEFINE_EVENT_TYPE_CASTS(typeName) \
     DEFINE_TYPE_CASTS(typeName, Event, event, event->is##typeName(), event.is##typeName())
 
 } // namespace blink
 
 #endif // Event_h