Fix mouse wheel scrolling on PDFs.

third_party/WebKit/Source/core/input/EventHandler.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2012 Digia Plc. and/or its subsidiary(-ies)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 1827 matching lines @@
     }
 
     return WebInputEventResult::NotHandled;
 }
 
 void EventHandler::defaultWheelEventHandler(Node* startNode, WheelEvent* wheelEvent)
 {
     if (!startNode || !wheelEvent)
         return;
 
+    Settings* settings = m_frame->settings();
+    if (settings && settings->wheelGesturesEnabled())

[bokan, 2016/03/30 19:01:50]

Is the idea that we first dispatch the wheel event, but if wheelGesturesEnabled
is true then instead of doing the default action and scrolling here, we should
scroll through the gesture pipeline? Do I have that right?

[dtapuska, 2016/03/30 19:15:45]

Yes that is correct; previously it was conflating the canScroll attribute which
caused issues with resent events in plugins.

+        return;
+
     // When the wheelEvent do not scroll, we trigger zoom in/out instead.
     if (!wheelEvent->canScroll())
         return;
 
     ScrollGranularity granularity = wheelGranularityToScrollGranularity(wheelEvent);
     Node* node = nullptr;
 
     // Diagonal movement on a MacBook pro is an example of a 2-dimensional
     // mouse wheel event (where both deltaX and deltaY can be set).
     FloatSize delta;
@@ skipping 2121 matching lines @@
 PlatformEvent::Modifiers EventHandler::accessKeyModifiers()
 {
 #if OS(MACOSX)
     return static_cast<PlatformEvent::Modifiers>(PlatformEvent::CtrlKey | PlatformEvent::AltKey);
 #else
     return PlatformEvent::AltKey;
 #endif
 }
 
 } // namespace blink