WindowServer: Add an IPC call for taking a screenshot

This patch adds Messages::WindowServer::GetScreenBitmap. It returns the
currently displayed on-screen bitmap as-is, as a Gfx::ShareableBitmap.

Userland/Services/WindowServer/ClientConnection.cpp

@@ -987,4 +987,10 @@ void ClientConnection::did_become_responsive()
     set_unresponsive(false);
 }
 
+OwnPtr<Messages::WindowServer::GetScreenBitmapResponse> ClientConnection::handle(const Messages::WindowServer::GetScreenBitmap&)
+{
+    auto& bitmap = Compositor::the().front_bitmap_for_screenshot({});
+    return make<Messages::WindowServer::GetScreenBitmapResponse>(bitmap.to_shareable_bitmap());
+}
+
 }

Userland/Services/WindowServer/ClientConnection.h

@@ -167,6 +167,7 @@ private:
     virtual OwnPtr<Messages::WindowServer::GetMouseAccelerationResponse> handle(const Messages::WindowServer::GetMouseAcceleration&) override;
     virtual OwnPtr<Messages::WindowServer::SetScrollStepSizeResponse> handle(const Messages::WindowServer::SetScrollStepSize&) override;
     virtual OwnPtr<Messages::WindowServer::GetScrollStepSizeResponse> handle(const Messages::WindowServer::GetScrollStepSize&) override;
+    virtual OwnPtr<Messages::WindowServer::GetScreenBitmapResponse> handle(const Messages::WindowServer::GetScreenBitmap&) override;
 
     Window* window_from_id(i32 window_id);
 

Userland/Services/WindowServer/Compositor.h

@@ -76,6 +76,8 @@ public:
 
     void did_construct_window_manager(Badge<WindowManager>);
 
+    const Gfx::Bitmap& front_bitmap_for_screenshot(Badge<ClientConnection>) const { return *m_front_bitmap; }
+
 private:
     Compositor();
     void init_bitmaps();

Userland/Services/WindowServer/WindowServer.ipc

@@ -123,5 +123,7 @@ endpoint WindowServer = 2
     SetScrollStepSize(u32 step_size) => ()
     GetScrollStepSize() => (u32 step_size)
 
+    GetScreenBitmap() => (Gfx::ShareableBitmap bitmap)
+
     Pong() =|
 }