LibWeb: Add ResourceLoader::load_sync()

This function creates a nested event loop and runs a load() operation
inside it, returning only once the load has either succeeded or failed.

This will be used to implement blocking loads (ew!)

Libraries/LibWeb/ResourceLoader.cpp

@@ -25,6 +25,7 @@
  */
 
 #include <AK/SharedBuffer.h>
+#include <LibCore/EventLoop.h>
 #include <LibCore/File.h>
 #include <LibProtocol/Client.h>
 #include <LibProtocol/Download.h>
@@ -45,6 +46,24 @@ ResourceLoader::ResourceLoader()
 {
 }
 
+void ResourceLoader::load_sync(const URL& url, Function<void(const ByteBuffer&)> success_callback, Function<void(const String&)> error_callback)
+{
+    Core::EventLoop loop;
+
+    load(
+        url,
+        [&](auto& data) {
+            success_callback(data);
+            loop.quit(0);
+        },
+        [&](auto& string) {
+            error_callback(string);
+            loop.quit(0);
+        });
+
+    loop.exec();
+}
+
 void ResourceLoader::load(const URL& url, Function<void(const ByteBuffer&)> success_callback, Function<void(const String&)> error_callback)
 {
     if (url.protocol() == "file") {

Libraries/LibWeb/ResourceLoader.h

@@ -42,6 +42,7 @@ public:
     static ResourceLoader& the();
 
     void load(const URL&, Function<void(const ByteBuffer&)> success_callback, Function<void(const String&)> error_callback = nullptr);
+    void load_sync(const URL&, Function<void(const ByteBuffer&)> success_callback, Function<void(const String&)> error_callback = nullptr);
 
     Function<void()> on_load_counter_change;