LibGUI: Start working on a GTreeView class.

LibGUI/GTreeView.cpp

@@ -0,0 +1,21 @@
+#include <LibGUI/GTreeView.h>
+#include <LibGUI/GPainter.h>
+
+GTreeView::GTreeView(GWidget* parent)
+    : GAbstractView(parent)
+{
+}
+
+GTreeView::~GTreeView()
+{
+}
+
+void GTreeView::paint_event(GPaintEvent& event)
+{
+    GFrame::paint_event(event);
+    GPainter painter(*this);
+    painter.set_clip_rect(frame_inner_rect());
+    painter.set_clip_rect(event.rect());
+
+    painter.fill_rect(event.rect(), Color::White);
+}