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 325 matching lines @@
         , movementY(0)
         , clickCount(0)
     {
     }
 };
 
 // WebMouseWheelEvent ---------------------------------------------------------
 
 class WebMouseWheelEvent : public WebMouseEvent {
 public:
+    // 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 RailMode {

[Rick Byers, 2015/03/18 23:30:58]

We'll want to use this from WebGestureEvent too I think.  Perhaps we should move
the definition into WebInputEvent.h?

[ccameron, 2015/03/19 00:05:10]

Good point -- done. Did this to the platform events too.

+        RailModeFree       = 0,
+        RailModeHorizontal = 1 << 0,

[Rick Byers, 2015/03/18 23:30:58]

these don't need to be flags, right?  I.e. it's not legal to specify
'RailModeHorizontal | RailModeVertical', right?

[ccameron, 2015/03/19 00:05:10]

The same is true of Phase, so I was guessing this to be a style thing. Changed
to non-flag-values.

+        RailModeVertical   = 1 << 1,
+    };
+
     enum Phase {
         PhaseNone        = 0,
         PhaseBegan       = 1 << 0,
         PhaseStationary  = 1 << 1,
         PhaseChanged     = 1 << 2,
         PhaseEnded       = 1 << 3,
         PhaseCancelled   = 1 << 4,
         PhaseMayBegin    = 1 << 5,
     };
 
@@ skipping 27 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;
 
+    RailMode railMode;
+
     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)
+        , railMode(RailModeFree)
     {
     }
 };
 
 // WebGestureEvent --------------------------------------------------------------
 
 class WebGestureEvent : public WebInputEvent {
 public:
     int x;
     int y;
@@ skipping 113 matching lines @@
         , uniqueTouchEventId(0)
     {
     }
 };
 
 #pragma pack(pop)
 
 } // namespace blink
 
 #endif