AK: Add NonnullRefPtrVector<T>.

This is a slot-in convenience replacement for Vector<NonnullRefPtr<T>> that
makes accessors return T& instead of NonnullRefPtr<T>&.
Since NonnullRefPtr guarantees non-nullness, this allows you to access these
vector elements using dot (.) rather than arrow (->). :^)

AK/NonnullRefPtrVector.h

@@ -0,0 +1,35 @@
+#pragma once
+
+#include <AK/NonnullRefPtr.h>
+#include <AK/Vector.h>
+
+namespace AK {
+
+template<typename T, int inline_capacity = 0>
+class NonnullRefPtrVector : public Vector<NonnullRefPtr<T>, inline_capacity> {
+    typedef Vector<NonnullRefPtr<T>> Base;
+
+public:
+    NonnullRefPtrVector(Vector<NonnullRefPtr<T>>&& other)
+        : Base(static_cast<Base&&>(other))
+    {
+    }
+    NonnullRefPtrVector(const Vector<NonnullRefPtr<T>>& other)
+        : Base(static_cast<const Base&>(other))
+    {
+    }
+
+    using Base::size;
+    T& at(int index) { return *Base::at(index); }
+    const T& at(int index) const { return *Base::at(index); }
+    T& operator[](int index) { return at(index); }
+    const T& operator[](int index) const { return at(index); }
+    T& first() { return at(0); }
+    const T& first() const { return at(0); }
+    T& last() { return at(size() - 1); }
+    const T& last() const { return at(size() - 1); }
+};
+
+}
+
+using AK::NonnullRefPtrVector;