Browser: Add basic back/forward history

Applications/Browser/History.h

@@ -0,0 +1,61 @@
+#pragma once
+
+#include <AK/Optional.h>
+#include <AK/String.h>
+#include <AK/Vector.h>
+
+template<typename T>
+class History final {
+public:
+    void push(const T& item);
+    T current() const;
+
+    void go_back();
+    void go_forward();
+
+    bool can_go_back() { return m_current > 0; }
+    bool can_go_forward() { return m_current + 1 < m_items.size(); }
+
+    void clear();
+
+private:
+    Vector<T> m_items;
+    int m_current { -1 };
+};
+
+template<typename T>
+inline void History<T>::push(const T& item)
+{
+    m_items.shrink(m_current + 1);
+    m_items.append(item);
+    m_current++;
+}
+
+template<typename T>
+inline T History<T>::current() const
+{
+    if (m_current == -1)
+        return {};
+    return m_items[m_current];
+}
+
+template<typename T>
+inline void History<T>::go_back()
+{
+    ASSERT(can_go_back());
+    m_current--;
+}
+
+template<typename T>
+inline void History<T>::go_forward()
+{
+    ASSERT(can_go_forward());
+    m_current++;
+}
+
+template<typename T>
+inline void History<T>::clear()
+{
+    m_items = {};
+    m_current = -1;
+}