Add rails to input wheel events.

public/web/WebInputEvent.h

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 155 matching lines @@
         // into WebCore, so round-tripping from WebInputEvent to a WebCore
         // event and back will not preserve these flags.
         CapsLockOn       = 1 << 9,
         NumLockOn        = 1 << 10,
 
         // Left/right modifiers for keyboard events.
         IsLeft           = 1 << 11,
         IsRight          = 1 << 12,
     };
 
+    // The rail mode for a wheel event specifies the axis on which scrolling is
+    // expected to stick. If this axis is set to Free, then scrolling is not
+    // stuck to any axis.
+    enum RailsMode {
+        RailsModeFree       = 0,
+        RailsModeHorizontal = 1,
+        RailsModeVertical   = 2,
+    };
+
     static const int InputModifiers = ShiftKey | ControlKey | AltKey | MetaKey;
 
     double timeStampSeconds; // Seconds since epoch.
     unsigned size; // The size of this structure, for serialization.
     Type type;
     int modifiers;
 
     // Returns true if the WebInputEvent |type| is a mouse event.
     static bool isMouseEventType(int type)
     {
@@ skipping 197 matching lines @@
 
     bool scrollByPage;
     bool hasPreciseScrollingDeltas;
 
     // When false, this wheel event should not trigger scrolling (or any other default
     // action) if the event goes unhandled by JavaScript. This is used, for example,
     // when the browser decides the default behavior for Ctrl+Wheel should be to zoom
     // instead of scroll.
     bool canScroll;
 
+    RailsMode railsMode;
+
     WebMouseWheelEvent()
         : WebMouseEvent(sizeof(WebMouseWheelEvent))
         , deltaX(0.0f)
         , deltaY(0.0f)
         , wheelTicksX(0.0f)
         , wheelTicksY(0.0f)
         , accelerationRatioX(1.0f)
         , accelerationRatioY(1.0f)
         , phase(PhaseNone)
         , momentumPhase(PhaseNone)
         , canRubberbandLeft(true)
         , canRubberbandRight(true)
         , scrollByPage(false)
         , hasPreciseScrollingDeltas(false)
         , canScroll(true)
+        , railsMode(RailsModeFree)
     {
     }
 };
 
 // WebGestureEvent --------------------------------------------------------------
 
 class WebGestureEvent : public WebInputEvent {
 public:
     int x;
     int y;
@@ skipping 113 matching lines @@
         , uniqueTouchEventId(0)
     {
     }
 };
 
 #pragma pack(pop)
 
 } // namespace blink
 
 #endif