LibWeb+WebContent: Add abstraction layer for event loop and timers

Instead of using Core::EventLoop and Core::Timer directly, LibWeb now
goes through a Web::Platform abstraction layer instead.

This will allow us to plug in Qt's event loop (and QTimer) over in
Ladybird, to avoid having to deal with multiple event loops.

Userland/Libraries/LibWeb/Platform/EventLoopPlugin.cpp

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Function.h>
+#include <LibWeb/Platform/EventLoopPlugin.h>
+
+namespace Web::Platform {
+
+EventLoopPlugin* s_the;
+
+EventLoopPlugin& EventLoopPlugin::the()
+{
+    VERIFY(s_the);
+    return *s_the;
+}
+
+void EventLoopPlugin::install(EventLoopPlugin& plugin)
+{
+    VERIFY(!s_the);
+    s_the = &plugin;
+}
+
+EventLoopPlugin::~EventLoopPlugin() = default;
+
+}

Userland/Libraries/LibWeb/Platform/EventLoopPlugin.h

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Forward.h>
+#include <LibWeb/Forward.h>
+
+namespace Web::Platform {
+
+class EventLoopPlugin {
+public:
+    static EventLoopPlugin& the();
+    static void install(EventLoopPlugin&);
+
+    virtual ~EventLoopPlugin();
+
+    virtual void spin_until(Function<bool()> goal_condition) = 0;
+    virtual void deferred_invoke(Function<void()>) = 0;
+    virtual NonnullRefPtr<Timer> create_timer() = 0;
+};
+
+}

Userland/Libraries/LibWeb/Platform/Timer.cpp

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/NonnullRefPtr.h>
+#include <LibWeb/Platform/EventLoopPlugin.h>
+#include <LibWeb/Platform/Timer.h>
+
+namespace Web::Platform {
+
+Timer::~Timer() = default;
+
+NonnullRefPtr<Timer> Timer::create()
+{
+    return EventLoopPlugin::the().create_timer();
+}
+
+NonnullRefPtr<Timer> Timer::create_repeating(int interval_ms, Function<void()>&& timeout_handler)
+{
+    auto timer = EventLoopPlugin::the().create_timer();
+    timer->set_single_shot(false);
+    timer->set_interval(interval_ms);
+    timer->on_timeout = move(timeout_handler);
+    return timer;
+}
+
+NonnullRefPtr<Timer> Timer::create_single_shot(int interval_ms, Function<void()>&& timeout_handler)
+{
+    auto timer = EventLoopPlugin::the().create_timer();
+    timer->set_single_shot(true);
+    timer->set_interval(interval_ms);
+    timer->on_timeout = move(timeout_handler);
+    return timer;
+}
+
+}

Userland/Libraries/LibWeb/Platform/Timer.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Function.h>
+#include <AK/RefCounted.h>
+
+namespace Web::Platform {
+
+class Timer : public RefCounted<Timer> {
+public:
+    static NonnullRefPtr<Timer> create();
+    static NonnullRefPtr<Timer> create_repeating(int interval_ms, Function<void()>&& timeout_handler);
+    static NonnullRefPtr<Timer> create_single_shot(int interval_ms, Function<void()>&& timeout_handler);
+
+    virtual ~Timer();
+
+    virtual void start() = 0;
+    virtual void start(int interval_ms) = 0;
+    virtual void restart() = 0;
+    virtual void restart(int interval_ms) = 0;
+    virtual void stop() = 0;
+
+    virtual void set_active(bool) = 0;
+
+    virtual bool is_active() const = 0;
+    virtual int interval() const = 0;
+    virtual void set_interval(int interval_ms) = 0;
+
+    virtual bool is_single_shot() const = 0;
+    virtual void set_single_shot(bool) = 0;
+
+    Function<void()> on_timeout;
+};
+
+}