Made PinchViewport a ScrollableArea

Source/platform/scroll/ScrollableArea.cpp

Index: Source/platform/scroll/ScrollableArea.cpp
diff --git a/Source/platform/scroll/ScrollableArea.cpp b/Source/platform/scroll/ScrollableArea.cpp
index 6c202a8dbb4331bf472e1c682f3ab5ea2def1f0f..52081fd9037eebfe6f8347af955e4eb9423dd279 100644
--- a/Source/platform/scroll/ScrollableArea.cpp
+++ b/Source/platform/scroll/ScrollableArea.cpp
@@ -422,6 +422,15 @@ 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);