Hide scrollbars when their dimensions are not scrollable.

Source/core/frame/PinchViewport.h

Index: Source/core/frame/PinchViewport.h
diff --git a/Source/core/frame/PinchViewport.h b/Source/core/frame/PinchViewport.h
index 4ab3a0246d63e1fb369b94916424311e8128b66a..827d28ae7be852409b79892b42143c5f1ccb2370 100644
--- a/Source/core/frame/PinchViewport.h
+++ b/Source/core/frame/PinchViewport.h
@@ -118,6 +118,12 @@ public:
     // scroll extents of the viewport within the document.
     IntPoint clampDocumentOffsetAtScale(const IntPoint& offset, float scale);
 
+    void adjustScrollbarExistence();
+
+    // Used in tests
+    virtual GraphicsLayer* layerForHorizontalScrollbar() const override;
+    virtual GraphicsLayer* layerForVerticalScrollbar() const override;
+
 private:
     // ScrollableArea implementation
     virtual bool isActive() const override { return false; }
@@ -139,8 +145,6 @@ private:
     virtual void setScrollOffset(const IntPoint&) override;
     virtual GraphicsLayer* layerForContainer() const override;
     virtual GraphicsLayer* layerForScrolling() const override;
-    virtual GraphicsLayer* layerForHorizontalScrollbar() const override;
-    virtual GraphicsLayer* layerForVerticalScrollbar() const override;
 
     // GraphicsLayerClient implementation.
     virtual void notifyAnimationStarted(const GraphicsLayer*, double monotonicTime) override;
@@ -167,6 +171,9 @@ private:
     FloatPoint m_offset;
     float m_scale;
     IntSize m_size;
+
+    bool m_hasHorizontalScrollbar;
+    bool m_hasVerticalScrollbar;
 };
 
 } // namespace blink