Fix mouse wheel scrolling on PDFs.

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

Index: third_party/WebKit/Source/core/input/EventHandler.cpp
diff --git a/third_party/WebKit/Source/core/input/EventHandler.cpp b/third_party/WebKit/Source/core/input/EventHandler.cpp
index 38065d3a1d549ae1df3bcd3c07ca47afd71e99c0..834a5d422175c22ddaa1369bfcb39159130595e3 100644
--- a/third_party/WebKit/Source/core/input/EventHandler.cpp
+++ b/third_party/WebKit/Source/core/input/EventHandler.cpp
@@ -1845,6 +1845,10 @@ void EventHandler::defaultWheelEventHandler(Node* startNode, WheelEvent* wheelEv
     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;