Add UMA metric to track the time saved on making events passive during fling

third_party/WebKit/Source/platform/PlatformTouchEvent.h

 /*
     Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies)
 
     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.
 
     This library is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 21 matching lines @@
         : PlatformEvent(PlatformEvent::TouchStart)
         , m_dispatchType(PlatformEvent::Blocking)
         , m_causesScrollingIfUncanceled(false)
         , m_shouldForceBePassive(false)
     {
     }
 
     const Vector<PlatformTouchPoint>& touchPoints() const { return m_touchPoints; }
 
     DispatchType dispatchType() const { return m_dispatchType; }
-    bool cancelable() const { return m_dispatchType == PlatformEvent::Blocking; }

[dtapuska, 2016/05/05 19:58:27]

ok this seems wrong to me; if listeners are forced to be passive; then it
shouldn't be cancelable.

+    bool cancelable() const { return m_dispatchType == PlatformEvent::Blocking || m_dispatchType == ListenersForcedNonBlockingPassive; }
     bool causesScrollingIfUncanceled() const { return m_causesScrollingIfUncanceled; }
     bool shouldForceBePassive() const { return m_shouldForceBePassive; }
 
 protected:
     Vector<PlatformTouchPoint> m_touchPoints;
     DispatchType m_dispatchType;
     bool m_causesScrollingIfUncanceled;
     bool m_shouldForceBePassive;
 };
 
 } // namespace blink
 
 #endif // PlatformTouchEvent_h