Made PinchViewport a ScrollableArea

Source/platform/scroll/ScrollableArea.cpp

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  * Copyright (C) 2008, 2011 Apple 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.
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 IntPoint ScrollableArea::clampScrollPosition(const IntPoint& scrollPosition) const
 {
     return scrollPosition.shrunkTo(maximumScrollPosition()).expandedTo(minimumScrollPosition());
 }
 
 int ScrollableArea::lineStep(ScrollbarOrientation) const
 {
     return pixelsPerLineStep();
 }
 
+int ScrollableArea::pageStep(ScrollbarOrientation orientation) const
+{
+    int length = (orientation == HorizontalScrollbar) ? visibleWidth() : visibleHeight();
+    int minPageStep = static_cast<float>(length) * minFractionToStepWhenPaging();
+    int pageStep = std::max(minPageStep, length - maxOverlapBetweenPages());
+
+    return std::max(pageStep, 1);
+}
+
 int ScrollableArea::documentStep(ScrollbarOrientation orientation) const
 {
     return scrollSize(orientation);
 }
 
 float ScrollableArea::pixelStep(ScrollbarOrientation) const
 {
     return 1;
 }
 
 } // namespace WebCore