LibHTML: Add ResourceLoader to support protocol-agnostic URL loading

We now support loading both file:// and http:// URLs. Feel free to
visit http://www.serenityos.org/ and enjoy the fancy good times. :^)

Libraries/LibHTML/ResourceLoader.cpp

@@ -0,0 +1,50 @@
+#include <LibCore/CFile.h>
+#include <LibCore/CHttpJob.h>
+#include <LibCore/CHttpRequest.h>
+#include <LibCore/CNetworkResponse.h>
+#include <LibHTML/ResourceLoader.h>
+
+ResourceLoader& ResourceLoader::the()
+{
+    static ResourceLoader* s_the;
+    if (!s_the)
+        s_the = new ResourceLoader;
+    return *s_the;
+}
+
+void ResourceLoader::load(const URL& url, Function<void(const ByteBuffer&)> callback)
+{
+    if (url.protocol() == "file") {
+        auto f = CFile::construct();
+        f->set_filename(url.path());
+        if (!f->open(CIODevice::OpenMode::ReadOnly)) {
+            dbg() << "HtmlView::load: Error: " << f->error_string();
+            callback({});
+            return;
+        }
+
+        auto data = f->read_all();
+        callback(data);
+        return;
+    }
+
+    if (url.protocol() == "http") {
+        CHttpRequest request;
+        request.set_url(url);
+        request.set_method(CHttpRequest::Method::GET);
+        auto job = request.schedule();
+        job->on_finish = [job, callback = move(callback)](bool success) {
+            if (!success) {
+                dbg() << "HTTP job failed!";
+                ASSERT_NOT_REACHED();
+            }
+            auto* response = job->response();
+            ASSERT(response);
+            callback(response->payload());
+        };
+        return;
+    }
+
+    dbg() << "Unimplemented protocol: " << url.protocol();
+    ASSERT_NOT_REACHED();
+}