Reset all EventHandler data members in EventHandler::clear()

Source/core/page/EventHandler.h

Index: Source/core/page/EventHandler.h
diff --git a/Source/core/page/EventHandler.h b/Source/core/page/EventHandler.h
index 5b54c150afc130623a9e41db5971bfff543345d2..299e56cbd81e157dc340524c5f375989512064d7 100644
--- a/Source/core/page/EventHandler.h
+++ b/Source/core/page/EventHandler.h
@@ -322,6 +322,9 @@ private:
     bool panScrollInProgress() const;
     void setLastKnownMousePosition(const PlatformMouseEvent&);
 
+    // NOTE: If adding a new field to this class please ensure that it is
+    // cleared in |EventHandler::clear()|.
+
     LocalFrame* const m_frame;
 
     bool m_mousePressed;