Selectively disable rubber banding on mac.

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 343 matching lines @@
     float accelerationRatioY;
 
     // See comment at the top of the file for why an int is used here.
     int scrollByPage;
 
     // See comment at the top of the file for why an int is used here.
     int hasPreciseScrollingDeltas;
     Phase phase;
     Phase momentumPhase;
 
+    // See comment at the top of the file for why an int is used here.
+    // Rubberbanding is an OSX visual effect. When a user scrolls the content
+    // area with a track pad, and the content area is already at its limit in
+    // the direction being scrolled, the entire content area is allowed to
+    // scroll slightly off screen, revealing a grey background. When the user
+    // lets go, the content area snaps back into place. Blink is responsible
+    // for this rubberbanding effect, but the embedder may wish to disable
+    // rubber banding in the left or right direction, if the scroll should have
+    // an alternate effect. The common case is that a scroll in the left or
+    // right directions causes a back or forwards navigation, respectively.
+    //
+    // These flags prevent rubber banding from starting in a given direction,
+    // but have no effect on an ongoing rubber banding. A rubber banding that
+    // started in the vertical direction is allowed to continue in the right
+    // direction, even if canRubberbandRight is 0.
+    int canRubberbandLeft;
+    int canRubberbandRight;
+
     WebMouseWheelEvent(unsigned sizeParam = sizeof(WebMouseWheelEvent))
         : WebMouseEvent(sizeParam)
         , deltaX(0.0f)
         , deltaY(0.0f)
         , wheelTicksX(0.0f)
         , wheelTicksY(0.0f)
         , accelerationRatioX(1.0f)
         , accelerationRatioY(1.0f)
         , scrollByPage(false)
         , hasPreciseScrollingDeltas(false)
         , phase(PhaseNone)
         , momentumPhase(PhaseNone)
+        , canRubberbandLeft(true)
+        , canRubberbandRight(true)
     {
     }
 };
 
 // WebGestureEvent --------------------------------------------------------------
 
 class WebGestureEvent : public WebInputEvent {
 public:
     enum SourceDevice {
         Touchpad,
@@ skipping 95 matching lines @@
         , targetTouchesLength(0)
     {
     }
 };
 
 #pragma pack(pop)
 
 } // namespace blink
 
 #endif