Allow objects without scrollbars to be scrollable

Source/core/platform/ScrollableArea.h

Index: Source/core/platform/ScrollableArea.h
diff --git a/Source/core/platform/ScrollableArea.h b/Source/core/platform/ScrollableArea.h
index a3cb10b3fb1aba567e696fa42dc4563b664934d8..2983fabd6d478b1fd7aa0210e2284221a7a6a6c0 100644
--- a/Source/core/platform/ScrollableArea.h
+++ b/Source/core/platform/ScrollableArea.h
@@ -132,7 +132,7 @@ public:
     virtual Scrollbar* horizontalScrollbar() const { return 0; }
     virtual Scrollbar* verticalScrollbar() const { return 0; }
 
-    virtual IntPoint scrollPosition() const;
+    virtual IntPoint scrollPosition() const = 0;
     virtual IntPoint minimumScrollPosition() const;
     virtual IntPoint maximumScrollPosition() const;
 
@@ -175,6 +175,9 @@ public:
 
     virtual void reportMemoryUsage(MemoryObjectInfo*) const;
 
+    virtual bool isHorizontallyScrollable() const = 0;

[aelias_OOO_until_Jul13, 2013/06/18 00:54:47]

Instead of making each subclass implement this, how about just checking if
visibleContentRect().size() is smaller than scrollSize()?

[bokan, 2013/06/18 23:03:27]

The meaning of this method is more "is the object allowed to scroll?", rather
than "is there overflow?". E.g. A RenderLayer isHorizontallyScrollable if it's
overflowX style is OAUTO or OSCROLL (and later if we want scrollable input text
boxes we'd add an "or isTextInputBox()"). I think it'll be different for each
subclass - though I think maybe renaming the method to something like
horizontalScrollEnabled() will reflect that better.

[aelias_OOO_until_Jul13, 2013/06/19 02:55:24]

So it really means scrollable by user input events.  Maybe rename to "bool
userInputScrollable(Orientation orientation)"?

[bokan, 2013/06/19 18:57:00]

Done.

+    virtual bool isVerticallyScrollable() const = 0;
+
     // Convenience functions
     int scrollPosition(ScrollbarOrientation orientation) { return orientation == HorizontalScrollbar ? scrollPosition().x() : scrollPosition().y(); }
     int minimumScrollPosition(ScrollbarOrientation orientation) { return orientation == HorizontalScrollbar ? minimumScrollPosition().x() : minimumScrollPosition().y(); }
@@ -205,6 +208,8 @@ protected:
 
 private:
     void scrollPositionChanged(const IntPoint&);
+
+    bool isScrollable(ScrollbarOrientation orientation) const { return orientation == HorizontalScrollbar ? isHorizontallyScrollable() : isVerticallyScrollable(); }
     
     // NOTE: Only called from the ScrollAnimator.
     friend class ScrollAnimator;