LibWeb: Move ImageDecoder client connection singleton to its own file

This will allow us to use it in more places around LibWeb.

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -195,6 +195,7 @@ set(SOURCES
     HTML/TagNames.cpp
     HTML/WebSocket.cpp
     HighResolutionTime/Performance.cpp
+    ImageDecoding.cpp
     InProcessWebView.cpp
     IntersectionObserver/IntersectionObserver.cpp
     Layout/BlockContainer.cpp

Userland/Libraries/LibWeb/ImageDecoding.cpp

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/ImageDecoding.h>
+
+namespace Web {
+
+ImageDecoderClient::Client& image_decoder_client()
+{
+    static RefPtr<ImageDecoderClient::Client> image_decoder_client;
+    if (!image_decoder_client) {
+        image_decoder_client = ImageDecoderClient::Client::construct();
+        image_decoder_client->on_death = [&] {
+            image_decoder_client = nullptr;
+        };
+    }
+    return *image_decoder_client;
+}
+
+}

Userland/Libraries/LibWeb/ImageDecoding.h

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2020-2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibImageDecoderClient/Client.h>
+
+namespace Web {
+
+ImageDecoderClient::Client& image_decoder_client();
+
+}

Userland/Libraries/LibWeb/Loader/ImageResource.cpp

@@ -5,7 +5,7 @@
  */
 
 #include <LibGfx/Bitmap.h>
-#include <LibImageDecoderClient/Client.h>
+#include <LibWeb/ImageDecoding.h>
 #include <LibWeb/Loader/ImageResource.h>
 
 namespace Web {
@@ -27,18 +27,6 @@ int ImageResource::frame_duration(size_t frame_index) const
     return m_decoded_frames[frame_index].duration;
 }
 
-static ImageDecoderClient::Client& image_decoder_client()
-{
-    static RefPtr<ImageDecoderClient::Client> image_decoder_client;
-    if (!image_decoder_client) {
-        image_decoder_client = ImageDecoderClient::Client::construct();
-        image_decoder_client->on_death = [&] {
-            image_decoder_client = nullptr;
-        };
-    }
-    return *image_decoder_client;
-}
-
 void ImageResource::decode_if_needed() const
 {
     if (!has_encoded_data())