LibWeb: Add a naive Resource cache

This patch introduces a caching mechanism in ResourceLoader. It's keyed
on a LoadRequest object which is what you provide to load_resource()
when you want to load a resource.

We currently never prune the cache, so resources will stay in there
forever. This is obviously not gonna stay that way, but we're just
getting started here. :^)

This should drastically reduce the number of requests when loading
some sites (like Twitter) that reuse the same images over and over.

Libraries/LibWeb/Loader/LoadRequest.h

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/URL.h>
+#include <LibWeb/Forward.h>
+
+namespace Web {
+
+class LoadRequest {
+public:
+    LoadRequest()
+    {
+    }
+
+    bool is_valid() const { return m_url.is_valid(); }
+
+    const URL& url() const { return m_url; }
+    void set_url(const URL& url) { m_url = url; }
+
+    unsigned hash() const { return m_url.to_string().hash(); }
+
+    bool operator==(const LoadRequest& other) const
+    {
+        return m_url == other.m_url;
+    }
+
+private:
+    URL m_url;
+};
+
+}
+
+namespace AK {
+
+template<>
+struct Traits<Web::LoadRequest> : public GenericTraits<Web::LoadRequest> {
+    static unsigned hash(const Web::LoadRequest& request) { return request.hash(); }
+};
+
+}