Start working on a Widgets library.

Widgets/AbstractScreen.cpp

@@ -0,0 +1,35 @@
+#include "AbstractScreen.h"
+#include "EventLoop.h"
+#include "Event.h"
+#include "Widget.h"
+#include <AK/Assertions.h>
+
+static AbstractScreen* s_the;
+
+AbstractScreen& AbstractScreen::the()
+{
+    ASSERT(s_the);
+    return *s_the;
+}
+
+AbstractScreen::AbstractScreen(unsigned width, unsigned height)
+    : m_width(width)
+    , m_height(height)
+{
+    ASSERT(!s_the);
+    s_the = this;
+}
+
+AbstractScreen::~AbstractScreen()
+{
+}
+
+void AbstractScreen::setRootWidget(Widget* widget)
+{
+    // FIXME: Should we support switching root widgets?
+    ASSERT(!m_rootWidget);
+    ASSERT(widget);
+    
+    m_rootWidget = widget;
+    EventLoop::main().postEvent(m_rootWidget, make<ShowEvent>());
+}