Extend ValueNode API.

- Add several new optional hook functions to ValueNode. These
  allow implementing subclasses to specify that they're a container
  type that can export a range of items (i.e. arrays, lists, etc.),
  and expose several operations on said ranges of child items.

src/apps/debugger/value/ValueNode.cpp

@@ -63,6 +63,34 @@ ValueNode::SetContainer(ValueNodeContainer* container)
 }
 
 
+bool
+ValueNode::IsRangedContainer() const
+{
+	return false;
+}
+
+
+void
+ValueNode::ClearChildren()
+{
+	// do nothing
+}
+
+
+status_t
+ValueNode::CreateChildrenInRange(int32 lowIndex, int32 highIndex)
+{
+	return B_NOT_SUPPORTED;
+}
+
+
+status_t
+ValueNode::SupportedChildRange(int32& lowIndex, int32& highIndex) const
+{
+	return B_NOT_SUPPORTED;
+}
+
+
 void
 ValueNode::SetLocationAndValue(ValueLocation* location, Value* value,
 	status_t resolutionState)

src/apps/debugger/value/ValueNode.h

@@ -51,10 +51,23 @@ public:
 									{ return false; }
 			bool				ChildrenCreated() const
 									{ return fChildrenCreated; }
+
 	virtual	status_t			CreateChildren() = 0;
 	virtual	int32				CountChildren() const = 0;
 	virtual	ValueNodeChild*		ChildAt(int32 index) const = 0;
 
+	// optional virtual hooks for container type value nodes such as
+	// arrays that may contain a variable (and potentially quite large)
+	// number of children. The calls below should be implemented for such
+	// node types to allow the upper layers to be aware of this, and to be
+	// able to request that only a subset of children be created.
+	virtual	bool				IsRangedContainer() const;
+	virtual	void				ClearChildren();
+	virtual	status_t			CreateChildrenInRange(int32 lowIndex,
+									int32 highIndex);
+	virtual	status_t			SupportedChildRange(int32& lowIndex,
+									int32& highIndex) const;
+
 			status_t			LocationAndValueResolutionState() const
 									{ return fLocationResolutionState; }
 			void				SetLocationAndValue(ValueLocation* location,