Browser+LibWeb+WebContent: Allow Browser to load local files

To achieve this goal:
 - The Browser unveils "/tmp/portal/filesystemaccess"
 - Pass the page through LoadRequest => ResourceLoader
 - ResourceLoader requests a file to the FileSystemAccessServer via IPC
 - OutOfProcessWebView handles it and sends a file descriptor back to
 the Page.

Userland/Services/WebContent/ConnectionFromClient.cpp

@@ -505,4 +505,22 @@ Messages::WebContentServer::GetSessionStorageEntriesResponse ConnectionFromClien
     auto session_storage = document->window().session_storage();
     return session_storage->map();
 }
+
+void ConnectionFromClient::handle_file_return(i32 error, Optional<IPC::File> const& file, i32 request_id)
+{
+    auto result = m_requested_files.get(request_id);
+    VERIFY(result.has_value());
+
+    VERIFY(result.value()->on_file_request_finish);
+    result.value()->on_file_request_finish(error != 0 ? Error::from_errno(error) : ErrorOr<i32> { file->take_fd() });
+    m_requested_files.remove(request_id);
+}
+
+void ConnectionFromClient::request_file(NonnullRefPtr<Web::FileRequest>& file_request)
+{
+    i32 const id = last_id++;
+    m_requested_files.set(id, file_request);
+
+    async_did_request_file(file_request->path(), id);
+}
 }

Userland/Services/WebContent/ConnectionFromClient.h

@@ -13,6 +13,7 @@
 #include <LibWeb/CSS/PreferredColorScheme.h>
 #include <LibWeb/Cookie/ParsedCookie.h>
 #include <LibWeb/Forward.h>
+#include <LibWeb/Loader/FileRequest.h>
 #include <WebContent/Forward.h>
 #include <WebContent/WebContentClientEndpoint.h>
 #include <WebContent/WebContentConsoleClient.h>
@@ -31,6 +32,8 @@ public:
 
     void initialize_js_console(Badge<PageHost>);
 
+    void request_file(NonnullRefPtr<Web::FileRequest>&);
+
 private:
     explicit ConnectionFromClient(NonnullOwnPtr<Core::Stream::LocalSocket>);
 
@@ -64,6 +67,7 @@ private:
     virtual void set_preferred_color_scheme(Web::CSS::PreferredColorScheme const&) override;
     virtual void set_has_focus(bool) override;
     virtual void set_is_scripting_enabled(bool) override;
+    virtual void handle_file_return(i32 error, Optional<IPC::File> const& file, i32 request_id) override;
 
     virtual void js_console_input(String const&) override;
     virtual void run_javascript(String const&) override;
@@ -91,6 +95,9 @@ private:
     WeakPtr<JS::Interpreter> m_interpreter;
     OwnPtr<WebContentConsoleClient> m_console_client;
     JS::Handle<JS::GlobalObject> m_console_global_object;
+
+    HashMap<int, NonnullRefPtr<Web::FileRequest>> m_requested_files {};
+    int last_id { 0 };
 };
 
 }

Userland/Services/WebContent/PageHost.cpp

@@ -263,4 +263,9 @@ void PageHost::page_did_update_resource_count(i32 count_waiting)
     m_client.async_did_update_resource_count(count_waiting);
 }
 
+void PageHost::request_file(NonnullRefPtr<Web::FileRequest>& file_request)
+{
+    m_client.request_file(file_request);
+}
+
 }

Userland/Services/WebContent/PageHost.h

@@ -66,6 +66,7 @@ private:
     virtual String page_did_request_cookie(const URL&, Web::Cookie::Source) override;
     virtual void page_did_set_cookie(const URL&, Web::Cookie::ParsedCookie const&, Web::Cookie::Source) override;
     virtual void page_did_update_resource_count(i32) override;
+    virtual void request_file(NonnullRefPtr<Web::FileRequest>&) override;
 
     explicit PageHost(ConnectionFromClient&);
 

Userland/Services/WebContent/WebContentClient.ipc

@@ -35,6 +35,7 @@ endpoint WebContentClient
     did_request_cookie(URL url, u8 source) => (String cookie)
     did_set_cookie(URL url, Web::Cookie::ParsedCookie cookie, u8 source) =|
     did_update_resource_count(i32 count_waiting) =|
+    did_request_file(String path, i32 request_id) =|
 
     did_output_js_console_message(i32 message_index) =|
     did_get_js_console_messages(i32 start_index, Vector<String> message_types, Vector<String> messages) =|

Userland/Services/WebContent/WebContentServer.ipc

@@ -1,4 +1,5 @@
 #include <AK/URL.h>
+#include <LibIPC/File.h>
 #include <LibCore/AnonymousBuffer.h>
 #include <LibGfx/ShareableBitmap.h>
 #include <LibWeb/CSS/PreferredColorScheme.h>
@@ -51,4 +52,6 @@ endpoint WebContentServer
 
     get_local_storage_entries() => (OrderedHashMap<String,String> entries)
     get_session_storage_entries() => (OrderedHashMap<String,String> entries)
+
+    handle_file_return(i32 error, Optional<IPC::File> file, i32 request_id) =|
 }